Well, personally. I would start with how well do you really know her? Do you like her because of her looks or her personality? Most girls are flattered when someone likes them, I know I am one. We love the attention. If you really want her to know, straight out tell her. That's how my boyfriend and I ended up together. I texted him one night and said "Hey I like you, okay bye." The rest is history.
Just walk up to her one day and say it, then walk away. Let it sink in, and then go ask her about it a little later and see what she says. If it doesn't work out, well than it's her lose. If it turns out she likes you back, well then good luck to you.
Hope I helped. :)