It looks like as you're lifting up you're bringing your hand/arm away from your body. Someone's tutorial says the motion of the lift up is sticking your hand on the small of your back, grabbing the hoop and you trace the back of your hand from your back, around/up your side as if you're wiping something off the back of your hand, then extend the arm all the way overhead, straight up. If you don't keep your arm close enough to your body it results in whacking yourself in the head with the hoop. Which I did a lot of.
Anyway, I tried to illustrate it in this short video first without a hoop, then slowly with a hoop, then in full motion with a hoop. Hope it helps! http://www.youtube.com/watch?v=DUha541S6dc