Generally it's about setting your body and legs more or less in a straight line and having them more or less parallel to the ground...
Body parallel to the ground + legs bent hanging down = stupid man deckgrab. This is what I end up doing all the time, haha. Name made up by Chris Bartnicki.
What is looking the worst is when someone has his body straight, bends his legs back and lifts his scooter high up there. I mean, wtf, this not only looks ugly, but lifting up the scooter is completely missing the point of this trick. A proper superman would be a trick when your whole body and the legs are over your scooter.