set your spin first and wait till you are in the air. when i was first trying to learn how to bring my knees up i tried to do it immediately off the jump and it would cause me to go off axis. practice on a trampoline some too. you will get it eventually its a fell type thing.
yeh, just practise tucking in your spins, don't grab too early and when you grab, make sure you carry on looking over your shoulder and don't look down at your grab, it'll stop your rotation.
Remember to have a good take off. THEN bring your legs up. Do it to early and your screwed. Eventually it will be one fluid motion. But just remember. Set first. Grab second.