How can I tease my girlfriend in sexual ways?
Kiss her neck, wrist, collarbone, thighs, earlobes, etc.
Tell her things you want to do to her.
Send her sexy text messages when you aren't together.
Run your hands along her body
Massager her with oils
nibble and kiss her ears, neck, stomach... depending on what you're willing to do... you can massage her boobs for a few seconds... gently grab her "down there"... or gently rub her "there"...