Say "hey, I like you." seems simple enough to me. :P you could always just ask her on a date and see what she says. If she doesn't believe you just keep pestering her until she does believe you. Slow and steady wins the race! :)
I truly hate to say it but you wanna let her know that you like her a little bit but don't let her know anything much for sure. Make her wonder a little bit it will increase your interest and you. Its the game. I hate the game but it kind of need to be played just a bit at first. A look and a smile can say plenty.
Just try to get her somewhere by y'all self cause if she don't like u her friends are gonna spread that u got rejected.but personally I don't mind it thru noye so that don't make it as weird but most girls just like u to say it.but just start hanging out with her and flirting and that kinda stuff.make sure if she's ur best friend dont ruin ur friendship.just tell her and give her some time to think don't keep asking her. Hope this helped:)good luck u can do it:)