How do I approach a girl I do not know?

This is something there are several situations where I feel I could use this information. Whether it be the cute 20 year old girl working at the Greek restaurant who smiles at me alot, or the shy quiet girl who sits alone in the lounge at school, or the amazing actress who rules the Drama department. I just don't know what to say! And when I try to start a conversation, I either get over excited or do something stupid like hug her the first time I meet her, or I completely shut down and do anything I can to get the hell out of there. Either way, I put my foot in my mouth. So what can I say to break the ice? How should the first conversation flow? How do I tell if we're on the same page? Btw, Just so you have more to work with, I'm 17. I love heavy metal. I love to preform on stage; plays, musicals, with my band, dance. I draw alot. I'm not in too bad shape. I wear gles. I'm a little corny and I'm kinda cynical and overly emotional, but I love my friends with all my being and put everything I have into a good relationship. I don't move too fast physically. I'm a little flamboyant. I love romance, tenderness, and cuddling. ^_^