How to Socialize Your Adult Cat
To socialize your adult cat, spend time in the room it's in without interacting with it so it gets used to your presence. After a day or 2, try encouraging your cat to interact with you by offering it treats. Once it comes up to you regularly, gently pet your cat on the back of its neck. When you're ready to introduce it to other people, start by keeping your cat in the same room as you and the new person, but make sure it has a place to hide, like under a chair. Then, play with your cat using one of its toys before having the other person take over. That way, your cat will associate meeting someone new with something it enjoys.
Let the cat have its space. When you're first getting to know a cat, it's best to let it get used to its surroundings. If you've just brought a cat home, give it a room where it can hang out and calm down. Leave it alone (with everything it needs) for about a day before you try interacting with it. Even if your cat isn't new and tends to hide, this method can be a good way for you to reintroduce yourself to the cat. Try putting a pheromone diffuser in your cat's room to make it feel more comfortable. Add a radio for company. A radio or playlist with gentle music (such as classical) may help the cat relax. It helps them feel not quite as alone. Play it softly so you don't annoy the cat, as cats' ears are more sensitive than ours. Hang out with the cat. To start getting the cat used to you, try just hanging out in the room with it. Don't try to interact with it yet. Just be in the room. Try reading a book, for instance, or just play on your phone. Sitting on the floor can make you seem approachable. Don't force them out of hiding. Give them a chance to come out. Also, stay relatively quiet, and don't make sudden movements that may startle the cat. Encourage interaction with treats. Once the cat is slowly getting used to you, try encouraging interaction with treats. You could place your hand on the ground and place treats around it. The cat will be encouraged to come up and take treats. Try gently petting the cat while you're giving it treats. If they're not quite ready to come out, try dropping a treat near where they are so they associate the treat with you. Play with the cat. Even if your cat is still being skittish, playtime may bring them out of their shells a bit. Try using a toy that has a stick with a fleece tail or mouse hanging off of it. Gently brush it back and forth near where the cat is hiding to see if you can encourage it to come play. You could also try wiggling your fingers under a blanket or using a piece of yarn to entice the cat to play. Work on petting. Once your cat starts coming out regularly to see you when you're in the room, you can start moving towards petting. Start by letting the cat smell you. Reach out a flat palm for the cat to sniff. If the cat rubs its head on it or seems interested, you can try petting it on the back. If it runs away, you may need to try again another day. Respond to aggression with gentleness. Sometimes, a skittish cat will show aggression because that is how it's dealing with being afraid. The important thing is to not yell or lash back at the cat. Just use a soothing voice and back up a little to give the cat space. Continue to talk to it for a few minutes. Don't just rush out of the room. If you just leave, that tells the cat that this behavior gets rid of the thing it's scared of--you! Set out a treat for it before you leave, so it still thinks of you in a positive light. Choose a gentle introduction. If your cat hasn't been around other people much, you'll need to start slowly. The first step is just having your cat be in the same room with someone new. Close off exits, though leave a hiding place in the room, and have your friend just sit and talk with you. That way, the cat can get used to the idea of someone new being around. Hiding spots can include places like underneath a chair or behind a piece of furniture. Play with your cat. One way to encourage positive interaction is to have playtime while your friend is over. Start with you playing with the cat (using a toy), and then get your friend to take over. Playtime will help your cat associate strangers with something they like. Try a few treats. Just like you got your cat to interact with you with treats, you can also encourage interaction with others with treats. Have the person sit on floor. They can place their hand down with treats nearby, which may encourage the cat to approach. However, remember that feeding your cat too many treats can lead to obesity. Cats should only have 20 calories per pound of weight each day to maintain their size, so a 10 pound cat only needs 200 calories a day. When you're feeding treats, make sure you're taking those into account for your cat's caloric needs. Try to pick treats with healthier ingredients. A shorter list of ingredients is better than a longer list. Also, skip treats that have preservatives and dyes. Let your cat sniff the person. The first part of interaction will likely be smelling. Your friend can even hold out a pointer finger for the cat to smell. Often, just offering it will get a cat to come over and take a good sniff. Keep in mind that some cats may need this introduction each time the person is over. If the cat seems interested, the person can try to pet it. Don't try to force the cat. Your cat should take the lead when it comes to interactions. If you try to force a timid cat to interact, it's only going to make the situation worse. However, if your cat can decide to come out on its own, that may make future interactions easier. Have a petting session. If you're trying to get a cat more accustomed to being petted, begin with areas the cat likes. For instance, if the cat likes its neck rubbed, start there. Move on to stroking parts it isn't quite as used to, such as the top of its head. Start with short sessions, and give your cat a treat as soon as you're done. Work on paws. Once you've worked on just getting the cat used to petting, start working on areas like its paws. Your cat will need its paws handled from time to time, such as when its claws are trimmed or when it visits the vet. However, most cats don't like their paws handled. Start by just touching the paws when the cat is near you or sitting on you (after some petting the cat likes), then work up to holding the paw in your hand. Keep the sessions short at first. Reward your cat with a treat afterward. Try doing this step when the cat is sleepy. Teach it not to struggle. Most cats aren't huge fans of being picked up, but it does need to happen sometimes. To help it learn not to struggle, pick it up. When it struggles, talk to it soothingly. When it stops struggling, you can put it down. If you put it down before it stops struggling, it learns that's what results from that behavior. Give them each their space. When you're first introducing pets, let them be in separate spaces. However, it can help to have a door between them, so they can sniff each other through the doors and start getting to know one another. You can also use a baby gate to keep your pets separated. Feed them on either side of the door. A good next step is feeding them together, but one on each side of the door. They'll be able to smell and hear each other, but they'll also be doing something enjoyable, eating. Avoid feeding them together when there isn't a door separating them. Sometimes, feeding animals close to each other can cause more aggression between them. Give the cat a chance to explore on its own. The cat will start to want to explore the rest of the house after a few days. The first couple of times it goes into the larger house, try locking up your other pets. That way, the cat can get the lay of the land without having to worry. Introducing the animals. After a few days or a week, try introducing the animals. Some unhappiness is to be expected. However, if they continue to be aggressive, you may need to separate them again by guiding the cat back into is separate space. If one of the animals is a dog, keep it leashed for the first couple of introductions. Always supervise the interactions in case the animals start to fight. Only let them out together when you're at home for the first couple of times. Watch their interactions. Before you let them out unsupervised together, all animals should be relatively calm. They should be able to eat and go to the bathroom without looking worried. If they continually fight, you may need to slow down the introductions and keep them separated for a while longer. 
Let the cat have its space. Add a radio for company. Hang out with the cat. Encourage interaction with treats. Play with the cat. Work on petting. Respond to aggression with gentleness. Choose a gentle introduction. Play with your cat. Try a few treats. Let your cat sniff the person. Don't try to force the cat. Have a petting session. Work on paws. Teach it not to struggle. Give them each their space. Feed them on either side of the door. Give the cat a chance to explore on its own. Introducing the animals. Watch their interactions. 