tell her your true feelings about her. Girls like when guys do that it shows that you care. And if she really is your friend she will tell you the truth. And sometimes it depends on how old you are. How old are you anyways?
OMG, all this douchebaggery!! Do NOT tell her your feelings!! That is so frikkin' lame!! To stay out / get out of the "friend zone", your approach should be bluntly romantic. You want her to know from the first moment you're not interested in "friendship", but that you want a romantic relationship with her. Now if she comes back with the dreaded "I want to be friends" line, you can either keep up the romantic heat... Or move on.
Honestly, this is a tough one because of the truth. If a female merely views you as a friend, you can be the kindest guy to her, you can treat her out and even buy her presents, but if she just doesn't foster feelings for you beyond friendship, then it's best to accept that she is not for you. If she likes you, then time will reveal that through her actions. You can always risk telling her how you feel, and maybe it will bring you closure to know how she truly feels. At the end of the day, you can't force someone to feel a certain way about you and, even if you could, I doubt you would want that. Maybe one day she will see you as more than a friend, but until then, just accept the reality of the situation.