if you got it, you got it. if you don't, you don't. you can't really change that fact. personally i must have the gift or something. i massage a guy's neck and they tell me within seconds how good it is. i just have that touch.
don't go too hard
don't go too soft
do you like her? then it'll be easier. you just get into it.
you probably shouldn't be massaging a random girl anyway. it's sorta wrong.