you could just try talking to her about something that interests her? it's easier to say what not to do then what to do lol, depends on the girl, i mean there are the obvious things like;
* be clean
* smell clean
* look at her face
* talk properly (we might say mumbling is cute but that's just to make u feel better)
* know her name
* NEVER start a conversation with what's you fav PvP game! was painful to watch a friend do that
* make sure she's single
* remember what she says... she will find a way to check you where listening latter
* NEVER tell her she reminds you of your sister or mother... or an family member
* if she says "ur like a bro to me" she's either worked out u like her and isn't interested, OR, Very rarely, she likes you but knows she shouldn't
* there is more but getting board of typing all this lol
also if she even slightly suspects you just want "the one thing" she is very likely to give you cold shoulder or slap u :/ sorry just the way of it