It varies from person to person, if you already know it's something your gf is into then I'd say in general women really respond to you describing what you want to do to them.
Approach it like actual sex, start with foreplay & really get detailed. Where you want your hands, how they're moving across her body, what your lips & tongue are doing to her, etc etc.
Concentrate on sensory input- whispering in her ear, the taste of her skin, your breath on her neck, hearing her moan, her back arching, yadda yadda.
Go into detail, I mean like get stupid detailed. Your hands- are you lightly tracing down her body with your nails or full on grabbing every inch of thighs that you can to pull her closer? Are your fingers drawing slow circles around her nipples or are you pinching them harder & harder? Does her skin feel soft on your skin or do you feel the goosebumps you're giving her? Beyond what you are making her feel, tell her how she's making you feel- tell her how hard she's got you, tell her how badly you want to slide your dick inside her, tell her it drives you crazy when you hear her breathing get faster & faster.