How do you tell a girl you love her without her throwing up and/or bursting into flames? Because there's this girl I know, and I really do love her.
Well, first I'd consider a lot of things. How old are you? Getting involved in serious love at an early age can be quite difficult, and the result is usually bad. Secondly, after observing this girl, do you believe she has feelings for you? You never want to rush into things to quickly, make sure she likes you. Ask her friends or just notice things like eye contact, constant laughing, or awkward movement while chatting with you, she may be getting nervous around you because you're liked.
This is the last step, and make sure you've followed the tips and have a good understanding of her. Go somewhere private with her, nothing too private, but not in public. Whenever you feel ready, tell her your feelings for her. The reason I don't recommend doing this in public is that she may feel uncomfortable answering in front of lots of people, and either deny or begin the experiences you listened in the beginning. Whether her answer is yes or no, ( If she answers at all, if she stays silent for a while then tell her that she may have as much time as she would like to consider, and that you apologize if this may seem awkward), do not get upset. In the event that she does say no, bring up the possibility that you could just be friends, and trust me, that's better then nothing. What's really important is that at the end of the day, go home smiling and remember that their are plenty of fish in the sea just waiting for you.