For many girls this is the easiest position to climax because she controls the action.
Your clitoris will receive most stimulation if you lean your torso forward, arch your back and push your crotch as close to the base of his penis as possible. By using a rocking motion your clitoris will touch his pubic bone. Since this is firm, the stimulation can be intense.
It’s also possible to sit up straight, move up and down and stimulate your clitoris with your fingers or a vibrator.
If you want your G-spot stimulated you have to lean back, resting your weight on your arms, while riding up and down on his penis.
If you don’t want to do all the work, you can lean forward, resting your body on your elbows and ask your lover to put his feet flat on the bed, bending his knees. He can then move his pelvis freely.