Take it slow... for a ton of guys... girls that are too sexual are untrustworthy, and you should be focusing on love and social factors rather than primitive sexual disires. If you just want sex... then firstly get to know him a little and then just tell him that your interested in him sexually not romantically... that way he would not be hurt in the end thinking that you actually had loved him... if he says no, then he has some dignity and is not for you :)
Just ask him for sex if u only like him sexually... however if u want ur cake and eat it too... = romantically + sexually + a proper relationship... then first try to give him open non verbal signs that u want to be approached... if he doesn't approach u... then u go up to him and start a convo... and then flirt with him as much as u can... if u just want to have sex -- appear as easy as u can if u want romantic + sexual relation-- dont appear too easy... good luck...
If it's just for sex then tell him. Or you can just get him somewhere quiet, flirt, then make out. If he's into it, lead him somewhere or have him lead you somewhere. This would probably work on all my friends so
Just be flirty, really flirty, and touch him a lot. Shouldn't take long for him to show interest, then pretty much just tell him to follow you and bring him to the bed, if he doesn't get the idea by then it's hopeless.