You need to bend his legs before the flip. Then you want to tuck his legs and arms in abit more, also trail his movements for smoothness. Meaning place the ends of the legs touching the onion skin of the last frame. also you need to ease in the air for gravity. Do faster frames then slow them down to a stop, then reverse it as he falls. He also needs to bend his legs when he hits the ground.
Im pretty crap at flips too but yeah hope that helps alittle.