how to sit on his face

He lies on his back on a level surface. On top of his face, you drop to your knees. This height may work for you, depending on how long your legs are, but you'll probably need to stoop a little. Don't lay your weight on his face, though, and continue to support yourself with your knees. With your hands on the floor or bed in front of you, support yourself while you lean forward. He will essentially be lying between your legs, beneath you, in a doggie position.

He might slide himself beneath so that his head is between your legs after you start in the same position (knees on the floor or bed, leaning forward comfortably with hands on the wall or bed frame). After that, you can get down on his face. You can either sit immediately away or begin by hovering if you'd like. When he needs air, when he wants more, and when he REALLY wants to be in there, he will communicate with you. It's important to communicate!