Here are some hints&tips on different quests you may encounter. Mind that the quests are assigned and skipped randomly, so you may well not see some of them for long, but meet some other perils.

The quests are small but no way simple. There are at least two finals in every quest. You win or you die, but in many of them, there are several ways to survive. You may fight or flee, or hide and wait for help, etc. Due to this and some inpredictability, the hints are surely incomplete. If you find a better way to complete a quest, please inform me or the Internet resource authorities, where you have found these hints. 

If there are other humans, their life and death often depends on you. Maybe you fail and die, or sometimes it may happen you die to save somebody?.. Watch for Harris quests, however. Usually they can't be skipped. Harris must not die at any cost, for the game would be over instantly. You may ask why - read the book, you should know... not only this, there are other tips in the original book, though you may save most or all of its heroes.

If you want to win quickly or like most the strategy part, you may quickly exit most of the quests, simply fleeing from the rats (some persons are besieged by rats, so they can't simply flee, usually their survival is the result of the most wise
actions possible). But it is not the best way. It seems, the better you play the quests, the quicker the researches are going, and it's quite hard to win without cheats and weapons that could become available due to research... And there is also
the final score measured in percents. If you reach the final, you may play again for the best result. Mine is 88% so far.

Now for the quests in order of increasing tension:

1. Lucy
You are a little girl delivering newspapers. You'd better not fight even a small rat. The street where you start is pretty safe, but the quest requires you to approach a rat-infested house. You may flee with the first disturbing noise though. You can
complete you job and leave newspaper roll in the house (who would ever read them?). You can also enter kitchen, remove the key and look into keyhole to see the evidence of the rats presence from some kind of a safe place. But it is not safe really.
Maybe there is more in this quest, it still awaits its heroes...

2. Errol Johnson
You are an aged man inspecting tickets in underground. You can kill a small rat, but no single man can fight the rat hordes for long. The train is late (due to rats swarming through the tunnel). You can wait for them, but this way you may well end up eaten, as you were in the book. The only way leads up. Not for long, though, the crowds of people would not let you pass to street. So you better hide. Your cabin is halfway up, there is a phone and a small rat in it. Call police, close the door. Better kill the rat, or it may turn the attention of the rat hordes to you (they would come anyway, but since your phone call, every second counts). Then hide in the cupboard (close it, of course). If you move quickly enough, the police would break in your hideout quicker than rats. Wait and see.

3. (some shopkeeper, I have forgotten his name).
You are an old man in your owned shop. You better not fight a rat. You are besieged by the rat hordes, so don't go to street. Unfortunately, there is no phone, and no help can be awaited. You have no impenetrable hideouts, so you have to flee. It
would be tricky though. Be sure all the doors and windows leading to the street are closed. Search the rooms for objects. You need some light. There are some chemicals somewhere, take them too. Close all the doors as you retreat to the cellar. If you meet a rat in the cellar, you have little time. If not, you may wait for a minute. When the moment seems right, mix the chemicals. The gas released will become your weapon and your armour. You may wait a bit before the rats retreat a little, then escape through the grating. If everything goes right, you will not meet more rats. Just go on and never look back, and you would be safe.

4. Keogh
You are a schoolboy (it is not quite obvious, but you study in Harris' class). Not quite strong, but you can do some damage even to a huge rat. You meet a big rat just killed a cat (so beware!). The rat would soon attack you, but you have some time
till it notices you. There is a brick nearby, for some weapon. You may throw it once, but if you do after the rat have seen you, you will likely miss. With a bit of luck, you can end with a rat in the canal water. But there woul come more rats, and you
have just one brick. So the main solution requires you to cross the bridge and climb the wall. Then you can get to the other side and to safety. If you get bitten, you would die of a disease later, so don't stand near the rat.

5. Paula Blakley
You are a woman with a baby and a puppy. You start with a big rat attacking the puppy. The puppy's fate is unrevealed, but since the rats bite carries disease that is almost fatal, you may consider the poor doggy lost. So don't ever attack the big mutant rats with your bare hands. There are more rats on the way, you can't fight them all. Tell neighbour to get help (she is now safe), go into house for the baby (now you better survive), take the knife (now you can attack the big rat, though there is always a chance the big rat bites you! So it is up to you whether to attack, it wouldn't help).
Now you can hide or flee. Fleeing gurantees survival of you and your baby. Hiding requires killing this nasty rat, closing all the windows and doors with you and baby inside. But the chances still are bad in the latter case...
 
6. Harris and the Rat
Meet Mr. Harris, an agile and clever school teacher. You are on a mission to catch a rat (it better be this huge mutant to continue research). The quest surely seems to be a hard one. There is also your co-operative rat killer. It is his profession in the first place, you are here to assist. You start in a van near some ruins and
a graveyard. It's late, better take some light. Open the van, but you must not lead the way. Even if someone tries to joke about you being scared. Eventually the man would come out, you may follow. There are no rat signs, but the rats would
be near the van soon, so do not dally more than it is needed. Follow the rat killer. When he nears the grave, a huge rat may attack him. Follow them quickly, that is into the grave and into the tunnel. Pick up all objects you find on your way, you need the cage for the rat and the keys for the van. When you reach the rat, your co-operative may be dead already (unfortunately, there has been no easy way found to do the job, one of you usually dies. Poor man was a bit too careless, may he rest in peace). The rat is busy though, and here comes your chance. Take the rat and put it in cage (you must carry the cage before). Do not go forward, the ruins are infested with rats. Retreat the way you came, till you reach the van. Enter the van and close it. If you meet no more rats on the way, you were quick enough to live this through. Now you may have a little rest. You can drop objects in the van (except the keys), you may wait for the rats to come and try to break into your van. Or you can start the engine and ride right away. If you have a rat in a cage, and were not bitten, it is surely kind of a way to go.

7. Tony

You are a kid. You can't fight a rat. You are besieged in your home alone. There seems to be no safe way out, so you have to hide and wait for help. However, you start with your home cat already have fought the rat, and now both are on the ground floor, while you are up in your room. Even worse, you are so small for a rat, that if it sees you, your movement is limited to the room you are in. So you can't run from the rat, but you have to deal with the rat in the house, and do it fast before other rats arrive through the openings. The only way is to outwit it, using its hunger. Wait a while, you would notice fearful shadows through the window. Be sure it is closed. Wait till you hear movement on the stairs. Take food (don't even think
of eating). When the rat enters, make sure your closet is open, then throw the food inside. When the rat follows, close the closet, and you now have some time to move around the house. Go down, there is a phone. Call police, and from now on you must
hold the house. Close all the doors. The cat has entered through the cat door, close it also. Look around the room, the poor cat is hiding here somewhere. Better close it, this way's safer for both of you now, for it can't help you. Now you can wait here, but if the rats are nearly inside, try to go upstairs, or keep moving up and down. The police must come in time and release you.

8. Harris and the kids
Harris' turn again, now he is with his class at school. The boys have seen many rats outside, soon they will besiege the school. You must, of course, survive, but you have to save your pupils. The school has several ways outside, and you must block them. But the attack is quite formidable, even for police forces to cope with it. So the main task is to call for help as quickly as possible. Go out (you can leave the pupils for some time safe in the classroom, however you must in all cases be near them on the stairs, or the panic will ruin your
efforts - and you are busy now to lead them anywhere safer). Make sure the pupils remain in your classroom. Go downstairs, open and enter staffroom, open and enter head's room. Phone police. Now time pressure is a bit lower, but you will be in trouble pretty soon (you have noticed the rats through the windows on your way?) There are still opened rat-ways. Close window in head's, enter staff's, close window, close head's door, go to stairs, close main door, close staffroom door. This order of actions requires high speed, but it allows you to call help quicker compared to closing the doors first, so it is better if practiced a bit. If all goes right, you'll end up with police call and doors&windows closed on the first floor, with no rats inside. If the rats are in, you'll have to try again.  Hmm... All doors? Well, no, for the boiler room is open. Enter boiler room, there may be a big rat inside. The rat wouldn't immediately attack, so the wisest way is to close the manhole inside to stop the last way for the rat hordes, then go to stairs and close the boiler room door. Still, you can kill the rat, but you most probably be bitten (not always). Try to test the bitten Harris case on your own, who'd know, maybe it's not game over, if the disease was researched already and the cure was found. It was not my case sure. On the stairs you have more time now, but there is a tricky job on hand, so don't wait for the rats eating through the main door, go up. You must get the class to the top floor, and quick. First go up and open top classroom door. Go down, open your classroom (if it was closed) and tell the kids to go to top classroom. Now you must lead them (each time you see the kids are here with you, go ahead a bit and wait for them again). If you find yourself unable to use stairs, for the panicking kids blocking the way, you have done something wrong, and it's as well as horror. If you end in the top classroom with your kids, it's all right. You can try to go down, to close your classroom, though it wouldn't probably distract the rats. If you go out, however, be wary. If you hear rats nearby, retreat to the top floor and into the classroom. After closing all doors possible, you have some time to wait. It's well if you hear sirens sooner than rats attacking the top classroom door, for you have the chances then. After the sirens the police would arrive, but they alone wouldn't be able to stop the rats. Then the fire brigade may come with water pumps. If they do before the rats break in, they could help, but you must warn them. Open the window and shout for help. Soon the fireman would arrive through the window and wash the vermin away downstairs.

9. Henry
The later in the game, the lesser explored quests you meet. You are Henry Sutton, a fit man. You were hurrying to work in the underground train, when something happened. The train is stopped and went on fire. Passengers ran out in panic, you are in the carriage with Jenny, your acquaintance. Soon the fire hell will be here, but you know what hell waits for you outside. Your chance lies in
between. Don't let the smoke to suffocate you. Take Jenny and go out. Don't run away, the rats would get you just like the other passengers you hear.
Open cabin and enter it, close the door. If there is a rat inside (or when it comes later), you can't fight with your bare hands and with Jenny to protect, so quickly leave and close the cabin, but remain near the train. When the fire destroys it, search about for some remnants, take the debris for some kind of a weapon. Now you must dare the tunnel, but this is tricky. Wrong time, wrong step,
and you are rat food. Move forward only when you think the smoke is overtaking, or when the rats nearby pay attention to you. If you step on the rat on your way, you are close, try to attack them quickly. Even if they run, it is well - they wouldn't counter-attack quickly. Just don't provoke them by wrong move. With a bit of luck, eventually, you will meet men, not rats, on your way.

10. Howard
Howard story, it seems, is linked to the nerve gas research, for it is effective weapon you could get closer to the game end. And like Harris, he must survive. It's not hard for him, too, for he has all the equipment in one room. Open the closet, wear mask, then protective suit and helmet. Soon the rats would gnaw at your door. Examine each button on controls, you can learn what they do. There is
a container with a canister with a virus. There is also a chamber with a gas outlet. If your protective equipment is on, you can let out the virus, then wait till the rats be at the door and let out the gas (mind that you have to press 2 buttons for each of these weapons to get into your room). When the rats are in, they would attack you, but there is some time till the rip your protective suit to pieces. If you can, add some more gas. The rats must die sooner than you.

11. Harris and the Rat II 
Harris time again. It seems, the rat HQ was located, and now you arrive here to find your friend and brother-in-arms came here first. It's good, for you may meet more than a single mutant, and you may have some help now. Look around, do you remember this place?.. The rats would be surely hiding in the darkness, so better find some light. Open the doors nearby, take electric torch (it is pretty bad, use it only in darkness and move quickly when it is on). Enter the kitchen, there is a cellar door. Locked. Get into other rooms, search things there. Eventually you'll find the keys amongst all the litter. Unlock the cellar and enter it. Now you have stepped into danger. Search about. The man came here and died, despite his axe, so the danger is considerable. Take the axe. If you wait a bit too long, you may have a rat on your back, and despite you wearing protective suit, it is goodbye. You may try to search about or you may try to enter kitchen and re-enter cellar just to check your back. It could also help to close the cellar door at last, to make it harder for the rats to attack you from behind. When you meet two huge rats in the cellar, attack them. They would retreat. Now is the time. There is a tunnel in the cellar wall. If you try to enter it, you'd stuck and meet the rat the way you wouldn't like. Take off protective suit and helmet (you'd look thinner), then go on, killing all the rats on your way, until...