Reading More Can Help Indirectly Boost Your Social Success
Since you're on this site you're already familiar with the concept of reading up on your problems to try to find advice on dealing with them. There's another way reading can help you. In one article I talk about how you can do a lot to indirectly improve your social success by making yourself a more interesting, knowledgeable, experienced person. One simple way you can that is by reading, something you may already do for fun anyway. Even if someone isn't reading due to a raw, calculated attempt at self-improvement they may still change in positive ways. Of course, the indirect improvement route can't totally replace real social practice, but it can certainly supplement it.
Besides from just helping you become more well-rounded and interesting in general, here are some of the things reading can help you do. Other forms of media may provide the same benefits, but in my experience I find reading helps the most:
You can catch up on social knowledge other people take for granted
When someone is socially inexperienced they often lack knowledge that other people naturally acquired as they grew up and hung out with their friends. Sometimes this makes them seem overly naive and innocent. They may just not be able to follow certain types of conversations either. Reading is a quick and dirty way to catch up. For example, someone may have been really sheltered in high school and college and be totally in the dark about what goes on at parties. They may not necessarily want to dive into that lifestyle themselves, but don't want to be totally clueless about them either. By reading a few books or websites on partying-related humor they could get up to speed.
It can help you understand and relate to people better
If you feel you can't relate to a certain type of person, reading books about them, or written from their point of view, can help you see how they tick, and learn that they're not the simplistic caricatures you thought they were. For example, someone may think people from a certain subculture are strange and obnoxious, read some books on it, and come away with a more nuanced, sympathetic opinion of them.
Free life experience
You'll learn a lot of things through doing them firsthand, but other knowledge and attitudes you can acquire through books or articles. You can read about other people's successes, failures, and realizations and not have to go through the same trial-and-error process yourself. Obviously this applies if you're reading a straight up advice book, but it also works for fiction. Someone could read about a character who's struggling to deal with his annoying family and pick up some ideas they could use on their bossy, over-sensitive co-workers. More generally, reading a lot also helps you flesh out your philosophies on life. Authors' attitudes towards the world show through in their writing, and you may like something you see and incorporate it into your own views (e.g., a perspective on the value of materialism).
What to read
In short, read all kinds of stuff. One rule is not to be too selective. If a piece of writing seems like it'll be enjoyable then go for it. A trashy biography of a rock star could still indirectly teach you a lot about how to socialize. Another guideline is to spend some time on topics you're not familiar with, but think it may help to know something about. Try to dabble in as many areas as possible too (while also accepting you can never learn every last thing). The more information you have crammed into your head the better. You never know when it will come in handy.
One thing that consistently surprises me is how you can be reading a book about one topic and come away with valuable lessons on a completely different subject. Someone may read a book on mountain climbing and gain insights into human relationships. A book on the first World War may teach you something about making friends. A weird piece of fiction may instill a more confident attitude in you.
If you're worried about your wallet there's no need to actually pay for books. Why do that when you can get an unlimited supply of them for free from the local library? Just go to yours and poke through the shelves. Check out the books that catch your eye. At worse they won't have a certain title and you'll have to wait a few weeks while they order it or request it from another branch. If you're not the type to re-read books then libraries will suit you fine. If you do like to take your time with your books, mark them up, or have them around for later, you can often get them cheaply from used book stores. Borrowing them from friends is also an option.
Some people who are really interested in self-improvement feel that the only titles worth reading are on direct personal development topics. They would see reading up on other stuff as an inefficient waste of time. The thing is, learning about all kinds of subjects is self-improvement too, for the reasons I already mentioned.
This article used a have a list of all these different genres or topics you could read. But really, it's not necessary. A good book or article from any category can be useful: Fiction, non-fiction, realistic, fantastical, whatever. The quality is more important than the genre. I'm not going to recommend any specific books either as it really isn't about that. It would really just be a list of books I like anyway. Dive right in and figure out what you like, and what helps you, for yourself.