Here's a clinch tip that works well for me: If you're shorter than your opponent, wrapping your wrists around his neck, squeezing and pulling down while you assault him with knees will make him struggle to let go, because it's hard for him to breathe, and rib shots HURT! BUT. If you're taller than your opponent, while you're hands are wrapped around his neck and tighten your grip, then with every knee you throw put your foot slightly behind when it left the ground. If you do it fast enough, you'll pull your opponent forward as you back up, giving him little time to attack as he's advancing and trying to block and dodge your knees.