Standing-up sex can be a challenge, unless there's some solid structure for support...like a door frame. For this pose, have your guy squat with his back against one side of a doorway. His thighs should be parallel to the floor, and he can put his hands behind his lower back for cushioning. Stand facing away from him, spread your legs so they're on either side of his, and then back up onto his member.
Once you're positioned, bend forward and push against the opposite door frame with your palms. This helps you balance and allows you to control your gyrations and vary the speed and depth of penetration. You're in the driver's seat, so mix up your moves — swivel your hips back and forth in a circular pattern or figure eights — and experiment to see what feels best. Every time you switch direction, you'll both experience new pleasurable sensations.
Leave on a pair of sexy stiletto heels...and nothing else. The shoes' shape will help keep you pitched forward on your toes for maximum maneuverability, and the mere sight of them will drive him wild.