Nothing. It just takes some courage and confidence in yourself.
If you can't muster the courage to even walk up and introduce yourself, why on earth would she ever let you inside her legs? A weak guy like you doesn't deserve a hot girl.
The solution is to become a strong guy. Strong guys get hot girls.
When you want something in life, you have to be willing to work your ass off for it. Amazing shit is not just gonna land in your lap. You must BUILD what you want. Do you want to be a strong guy? Then BUILD it! Don't ask "But how?" Just get started.