Do you have a cat that never comes out from under the couch? You're not alone. A lot of cats can be really fearful around people or other animals or especially if you have guests or change the environment. If that's the case, one of the first things you want to do is really figure out what your cat's triggers are. Once you know that, avoid triggering your cat as much as possible while you teach your cat to be comfortable. If your cat hides under the sofa or under the bed all of the time and is very fearful of people, you really do need to be very calm, cool, and collected with that cat, because the more you pressure them by trying to touch them and tell them everything is OK and show them that you're friendly, the more you're going to scare that cat.
The best thing you can do is, every time you walk by give them a couple treats and otherwise leave them alone. If they happen to come out, toss them some more treats. But the best thing to keep in mind is: play hard to get. If you play hard to get with a cat that's fearful, you have the best chance that they're going to come over to you and want touching eventually. But first, make sure they really want to come over to you and get some treats.
Otherwise, just make sure that that cat who is hiding has easy access to food, water, and litter boxes, because if they're very fearful they may be afraid to go to those places where they meet their normal needs. If that doesn't help in a few weeks, make sure to talk to your veterinarian. And that's how you get started with a fearful cat.