In these situations, the best thing to do is to cut off contact with them. You're not obligated to endure abuse, even from members of your immediate family.

If these are more distant relatives who only show up around holidays, then it's time to tell your family that you're not coming home for Thanksgiving (or whatever).

If you're living at home, it's time to make a plan to GET OUT. Secure enough financial resources to move out of that house. If you're under-aged, then you can make a plan you can execute on as soon as you're 18.

A few people have mentioned it obliquely, but I'll come out and say it: Flat out refuse to accept a long-term guest.

It's one thing if a friend is visiting from out of town for a weekend (heck even a couple of weeks), as long as you know they're headed back again.

It's another thing entirely if they're moving to your area and "need a place to stay until they get settled". Same thing goes for new friends in your new town. Don't let people crash at your place.

This is really hard advice to give or to follow, because you'll feel like a monster when someone asks you for a place to stay and you say no. However, if you don't set a hard line on this, you're going to wind up with a roommate who doesn't pay the rent.

If it's ambiguous, then set a hard exit before letting them in "Of course you can crash at my place for the weekend. I can totally put you up until the 15th!". Setting clear expectations makes it easier to point out that they've overstayed their welcome.

• You need a budget. You can make your own, or sign up for youneedabudget.com (not an advert, I use it and it transformed my personal finances).
• Learn to cook a few simple meals that you enjoy. Focus on things that are easy to make and/or freeze well. Restaurants/take-out are an expensive luxury. It's fine to order food once a week or so (if it's in your budget, see above), but don't make it your primary source of food. Seriously you don't need to be a chef to figure out how to make some basic meals.
• Craigslist, facebook marketplace, and thrift shops are great places to get essentials for cheap, particularly kitchenware. Keep an eye out for a week or two to get a feel for each in your area, then start contacting about listings you find interesting.
• Get a first aid kit and a fire extinguisher. Put them both out in the open where someone else can find them easily. The extinguisher should be near (but not inside) your kitchen.
• If your apartment is above ground level, then get an emergency ladder. The ladder doesn't have to reach the ground if you're high up. It just needs to let you get a story or two down/up, or to a nearby balcony.
• Select furniture that rolls, breaks down, or packs flat. Your mattress should be the bulkiest thing you own. This will make moving a LOT easier in the future.
• Don't paint your apartment. It's not worth it to paint back to greyige when you leave.
• Are you in high rises or other corporate-owned apartments? You can save yourself a LOT of money if you're willing to move around. When your landlord raises the rent (and they will, at the 1 year mark) move to another apartment in a different building. Take advantage of discounts like free months or introductory rates, then do it again a year later. People hate to move. So landlords offer sweet deals to get you in the door, and then take that deal away once they've "got" you. If you're not afraid to move you can save a TON of cash by bouncing apartments once per year.
• Apartment living is a great time to practice minimalism. The faster you can pack out, the more free you are. I used to be able to move (like, start to finish) in about 2 hours. This works great with the tip above.
• Despite the advice I just gave about Minimalism, this is your home. You should like how it looks/feels. Go a bit beyond just "functional". Avoid creating a bachelor pad. Add a little bit of décor, pick a few pieces of nice furniture, and try to move the feel of the place towards "neat" instead of "empty" or worse "a guy lives here". You should like how your place looks when you come home.
• Set yourself a wakeup time and (more important) a bedtime. Yes, like you're a kid. Why? Getting enough sleep is an essential part of good mental health.
• Make. Friends. Once you've got your apartment worked out, go out and socialize. Find clubs based around mutual interest and start participating in them.

It's a misconception that Introverts don't like people. Introverts can be very sociable. Introvert vs. Extrovert is about where you get your energy and where you spend it. Introverts recharge by having time alone. Extroverts recharge by spending time with others.

If having time alone is draining, you're an extrovert. If you like people/crowds but need to take a break after an hour or two, you're likely an introvert.