Cats which grow up without contact with people can hardly be called domesticated if they don't learn to enjoy human society, being kittens, it will be difficult to teach them and this process is rarely effective.
Cats which grow close to people but for some reason had to do on their own for some time, can be taught to accept human society. But cats do not have labels «I was thrown out of home at early age», that's why you have to start working with them equally.
When you start this you need two things. First, patience, and, second, key factor. Patience is very important, because domestication of any animal takes as much time as needed. And it depends on the cat whether it wants to trust you or not. You cannot make it trust you and if you try to do it, the results will be delayed, maybe irreversibly.
There's something one should understand. The reason why cats in most cases survive among wild nature is that they are frightened, more often they run away than fight, retreat than investigate and in general they are rather conservative. They appear in your house the way they are — wild frightened animals leading night way of life. Otherwise, they won't live independently even a week. One should spend time, maybe much time, reeducating cats and the result may be domesticated wild cat and not a domestic cat. Remembering this let's continue.
Speaking about key factor we mean that you must have what your cat means, and then it will be possible to influence its behavior. Usually food plays the role of key factor. A reliable source of tasty food is such a force which cannot be resisted by animal, especially if it survived during some time depending on its own.
Feed your pet twice a day by separate portions. You will become a very important person, of course, you bring food. At the beginning do not try to come closer and look at it. Just enter the room, leave the food and walk away. Talk to your pet in a warm and quiet voice all the time. Try to say the same words each time, then it will become a component part of sedative ritual for your pet.
Continue to act this way till your cat feels freely when you enter the room. If it comes up to you in anticipation of lunch, it will be great! But even if it just sits without hiding somewhere or shrinking of fear, you may take it as a victory. If it turns its head and watches you, it is an excellent sign that it, at least, is not frightened so to lose its ability to move. Cats' eyes will show you the secret of its inner world. If the pupils of the eyes are extended, it means that it is still scared. If they are of normal size under present conditions of light, it means that it is calmed down. As soon as you reach such effect, come closer to your pet giving it food. Talk to your cat. Familiar sounds will help it to relax.
Spend as much time in the room as possible and try to do as less as possible. You may read. During these visits try not to look at your pet and not to touch it. Even if it gets into contact with you, let it happens on its terms. Allow it to investigate everything without moving towards it and looking at it. It wouldn't be a bad thing if you take some tasty things. If a cat comes to you, give it some. Even if it eats later, it's a good result. Of course, during some time, it will become quieter and will eat everything in your presence. But your smell won't give a special pleasure.
Turn on a radio or a TV-set, setting them on a low volume so that your cat gets used to human voices' sounds. Record your own voice and let your pet listens to it while you are not at home. Read something in a quiet and low voice. All this will be very useful.
If all your efforts are not rewarded and your cat after two weeks are still frightened as it was at the beginning, consult a vet. There are some effective and safe medicines which can help your cat to calm down in a sufficient degree so that it can learn to enjoy your presence.
If medical treatment doesn't help, one should make an effort and organize a corner for a cat where it can live peacefully and nobody disturbs it. Such safe refuge may be a large cage near the house or in the garage. There must be bars for climbing and secluded corners in the cage where it is possible to hide.
But if there is no possibility to organize such shelter and everything you've done before, doesn't work, then you face a difficult choice. It's not humane to make a cat live in fear. It's also not humane to bring it back to the street where it can be exposed to the risk because of the weather, dogs, toxic substances, illnesses and other cats. The most humane and at the same time the most difficult choice is euthanasia. Such decision is hateful for us but, however, it is better than if a cat dies slow and painful death on its own.
Top safety, please!
Scared and uneasy cats, also the cats, which you got not long ago, may try to run away. Make sure that all the windows are densely closed and are protected with good nets firm enough to stand the weight of your cat.
Do in such a way that between your pet and street there are at least two doors. Cats are strikingly quick animals when they want to be.