What would you do if your friend like this girl but she looks at you a lot?

Just because a girl looks at you a lot does not mean she likes you. Maybe she finds you physically appealing.
If she's with your buddy, than back off, until the time is right.

A girl look at you a lot doesn't mean she likes you, even if she does it doesn't mean she will like your friend. It's better to find out who she likes before you make this "I'm not going to take my friends girl" move, After all your friend could be doing the same thing(not going to take my buddy's girl) if he know you like her too.