Read a book, take a class, find a hobby, hang out with people who challenge you intellectually, travel...
I just read your additional info., you just sound like you are worried about carrying on interesting conversations with people. Lots of people have that problem. I would still try to do all the things above, but mostly you just have to relax and try not to worry if you don't have anything to add. I used to be really shy and didn't think I had much to say. I forced myself into uncomfortable situations and after a while I just became more confident in speaking with others. Also, I learned that a lot of people just want to talk anyway, so a good start at learning to make conversation is to really listen and then ask follow-up questions.