I have always been seen upon as shy, but I didn't think so myself. It was just that I didn't feel like talking. "You don't talk enough" must be the phrase I've heard most often. But I know that I sometimes talk too much as well, if there is something I have a passion for, and know a lot about, I can go on explaining it until I realize that people is getting very bored. Or if people ask me anything that is about facts, anything I can give an concrete answer to.
In social situations with several people I mostly tryed to listen and follow the conversation, or just fall of, and think about other things. Lately I have given up, and I listen to or interact only on what i'm intrested in. It actualy became a whole lot easier with that approach, because I don't feel so much pressure, and can use my energy otherwise.