If you are under 18, YOU SHOULDN"T. If you are of the proper age, you should do so gently at first, then ask her what she likes. It makes you look like a caring partner and you won't have to wonder...
You tell her how you feel and you attact here and lick them kiss them hug them squish them press them hold them oh and then you have sex with her to celebrate!
depends how old you are and how comfortable you are with each other. But i would say yesif she doesn't mind it all depends o your gf and if your scared to ask her look for sign's if she touches on...