Well if this girl knows you well it will be easy if she doesn't it WILL be hard

Try complimeting her say she has awsome shoes or cool hair something like that
Tease her a little and then smile at the end
If you are ready to tell her and your to shy tell a friend to tell her
For her birthday (if you know it) say happy birthday and smile of course
Make jokes about the poeple you and her hate
If your around her friends don't tease her friends it will only make things worst
If one of the girls your cool with fall down look caring (but not too caring or she'll think you like her) girls love that
If you know the girl likes a type of guy like bad boy don't try to act really bad just like play foot ball or sports and tease people but in nice ways
Try to kinda make ecues to see her but not to obivos like if you have a friend siiting nerby talk to him but first think of something to tell him
Show that your brave if you have a dobge ball team and they play rough try winig the team(or anything else brave)