Im assuming that you are a girl? You should clarify this, as over 95% here are guys and the site is generally guy oriented.
One thing I need to ask, are you hot? Are you fat? If you are hot, then great, if you're fat, then I can hopefully help you with that. That's off topic though.
Back to my intended ONE THING that you need to know: In High School, people like people that like them. Percieved value is of course added to this, but that is generally how it is. Value + emotions (generally for attracting girls) + showing interest, often = attraction.
Value to a guy is of course, your looks and your reputation ("She's a *****" "She's the hottest one" etc). Like me, guys don't want their friends to think bad of them, but good of them, based on what girls they hook up with. This is why Im often in indecision about whether to go for a girl or not.
It's also nice if you put out, if you know what I mean.
So lets get to the point. To be honest, just go say hi; however, I know you probably wont do that. Something else that can be really hot is if you catch eyecontact with him, hold it and smile. Im sure other people here can think of something. If nothing works out, please approach him and see what happens.