Bend your knees. Deep. It sounds simple and I'm sure you think you already have a good knee bend. I thought I was bending my knees enough too. However, I watched a video of myself and I noticed I was too upright. For a long time I have struggled to understand why my forehand didn't get the kind of depth, height, and spin that I wanted. The moment I focused on getting more kneed bend, I was clearing the net by 3-4 feet and the ball was dropping in the court and kicking up high. It also had more pace than usual. Even if you think you have good knee bend, give this a shot next time you play. Your legs should be around halfway between parallel to the ground and upright, your butt should stick out a little, and your torso should be at about a 45 degree angle. I kept this knee bend even while not hitting the ball. For those who are weightlifters, you're basically in a squat position but with your legs a little above parallel. Only problem with this is your legs can get pretty tired from holding this position.