If you are feeling shy, a really good way to get around this is to pretend not to be shy! I know it sounds kind of crazy, but this really does work. How do you do it? By practicing. Try it out with a close friend or someone in your family. Practice out loud what it is you might want to say to someone. When you get in a social situation, just go for it and try to participate. Remember, even the people you think are outgoing probably feel just as nervous as you do. The difference is, they put themselves out there anyway. It's okay to stumble over your words or make a mistake—everyone does. Just cut yourself a break and keep trying.
If you are not sure you want to jump right in, try just being involved in a conversation that is going on. Add as much as you feel comfortable. Why not start by smiling and saying,"Hi"? Most people you approach will probably be glad that you did! Ask them about something that they are interested in or mention something that you have in common. The conversation will probably go fine from there. It is also easier to learn to talk with people if you get involved in an activity that interests you so that you work together on common goals and interests, and you'll have real things to talk about.
You can do it! (:
