Try roleplay. You know better than us what your gf likes, so make up a scene in your head which plays to her desires. There's no hard and fast rule, some girls actually prefer unadulterated filth, but I would say the majority like to be romanced a little. Take a cue from Mills and Boon, and make it your own. Then just send her detailed texts explaining the scene in your head, the more detail the better, and by and large i'd say proper grammer, spelling and punctuation is your friend.