Twirl, Bite, & Act Sweet

Odd title, yes I know.
But one way to get a guy's attention and let him know your interested is, especially if he's watching you, make eye contact for one thing. Do puppy eyes with a little smile and, if you feel the need, bite your lip a bit. Also, don't be afraid to twirl your hair.
I think the eyes is one of the most important things, for if your eyes look angry or not welcoming the boy might get the wrong impression and back off.