How do I stop ignoring people?

The best thing to start with is just smile or give some sort of greeting to those you know or talk to on occasions most of the times when you see them. If they're social, they'll come to you. Also, hang with your close friends more when they're with one or two other friends. I went to the movies with a friend and she brought along this girl i never met. When me and my friend started talking, she joined in and we found something we're both interested in and became friends. Don't go if you only know one person out of a group of ten or something because you'll just be out of the conversation then.