-Watch how she acts around you
If you guys were friends before, if she knows you like her there may be more awkward silences. She may also avoid you a bit, even if she is interested, because she's not quite sure what to do.
- if you guys are still friends, well then, great. Take it up from there.
If you guys weren't really friends before you liked her, the girl will probably not say or do anything that will let you know. Girls can be annoying that way. She may talk to you more, or completely ignore you. Basically, any drastic change in behavior is a good sign that she knows.
-Think about who you've told before
If you told any of her friends or any of your friends that you both have in common that you like her, chances are she knows.
-If she knows and does like you back she will talk to you more, walk near you, sit next to you, make eye contact, twirl her hair, or give you compliments. She may also be secretive about who she likes.
You may want to avoid her for some time to see if she eventually talks to you but you are making one of the biggest mistakes you can.You should talk to her more and that way she might be the one to say, "I like you" first.
Be direct about telling a girl you like her; don't beat around the bush. Don't say it the day you meet her, but if you guys have been chatting for a month or more go ahead and make a move. She might fall for someone else if you wait too long.
Make friends with her friends. They will talk about how great you are and she may notice you more. But be careful, some friends will only gossip about you and make you look like a fool, so choose carefully.
Be charming and nice, but don't crowd a girl; they find it very annoying. Make casual conversation but don't follow her around or talk to her too much