Well I don't know if you're serious about her or not.

If you just wanna hook up with that girl, just for sex, then its wrong. Don't try to ruin someone's life.

I'm in the same dilemma

I had a crush in the past, I tried impressing her, tried to talk to her everyday (but she ignored), helped her indirectly in many ways, and many more stuffs.
I even proposed her after 2 years, but all she said was a big NO. I don't what might be the reason behind it, but I was very much heart broke for more 2 years. In this 2 years, I completely engaged myself into my hobbies & studies and turned anti-social. I also tried analyzing what mistakes I did.

Although I've helped few of my friends in such situation but only if they are serious about it and not gonna do this for "timepass".

Anyways, the advice.

1. First, forget yourself, who you are, etc.
2. Pretend to be a nice person in front of her, that's because, even if you're a pathetic trolling faggot, just because of her, you'll change yourself (believe me, I did change). Try to let her know you and vice-versa.
3. Try to cool and don't let the nervous breakdowns occur when you're talking to her.
4. Try to crack some silly jokes on her (not major ones, but just lame simple jokes) and let her smile for a while on your stupidity (it sounds awkward, but it helps).
5. Try to look straight into her eyes (if you can't, then you can be assured that you really love her from the bottom of your hear & you feel shy about it. But its time to be a man and look straight in the eyes and talk).
6. Don't let any of your friends know about this. Because if you tell the whole world about it, chances are there that she may become upset of people calling her with your name or vice versa. You should let everyone know about this only when you have either proposed her or dating her.
7. When everything is alright and you have confessed her about your love for her and if she accepts your proposal, then by this time, you'd be a changed man (from a trolling faggot to a sensible man who respects others).
8. If #7 point ^ becomes true then start introducing her between your friends (and family).
9. At this time you should be able to decide the further stages.

I don't know if its really gonna help you or not, but I'm at step 6. All thanks to Esotorisk

I'm gonna wait for few more weeks and then propose her as I'm in deep love with a girl.