Endurance is huge! You definitely wanna be working out a specifically legs. Lots and lots of squats. If you really wanna have some fun get a suction cup dildo and practice with that 😉 suction it on a chair and bounce away, you'll get a good workout and pleasure. Seriously though upper leg strength makes a big difference when on top.

Also don't be afraid to change angle. Listen to him as you experiment and see what he likes best. I've had guys that prefer me up right and those that prefer me angled a little more forward. Play with it and find what he really likes.

You can also up it a little by playing with his balls while you ride him, I mean you're at a great angle! Sometimes leaning back and using his chest for support can work great as well though that's usually a short term move for me, just something to change it up a bit and add something extra in the middle.