Personally, I first try to figure out what they might feel about me. If you go about that, keep in mind that she could be keeping her own feelings for you secret, so don't get discouraged if you can't get anything definitive. I also would try some light flirting and see how they respond (or let them know I'm interested if they wanna make the first move). Something like a slightly longer hug than usual, giving them a special smile, compliments to let them know how special they are ("You're so cute.", "I don't know what I'd do without you.", ect.), certain intimate (non-sexual) contact like playing with their hair or a shoulder rub, uh... it's really late so I don't really remember anything else @_@. Hopefully you get the idea :'P. Women tend to pick hints and body language pretty quickly so it should help :'P.
Then there's also just straight-up telling her that you have feelings for her. It's quick and to the point :'D. If she unfortunately doesn't share these feelings, don't get discouraged. Instead, be proud that you at least gave it a shot instead of leaving it at "what if?".
