Cork 7 was the first that I learned. When you do it off a jump think spin instead of flip. When I first started learning them I would throw it way to hard downwords and end up flipping out like crazy. Pretty much just throw a 720, but look at your tails and tuck.
If you have yet to take it to snow, don't be too nervous about hurting yourself. I ate it probably 6 times learning it on snow because I was too dumb to try it on a bag first first and never sustained any injuries. Whatever you do, make sure you tuck and don't pull the parachute mid cork, as you will land in a much more painful position.