I started with ENO slap straps. Unfortunately they are heavy and stretch, especially when wet. I woke up with buttocks firmly on the ground a couple of times.
Now I suspend my hammocks with a combination of whoopie slings from whoopieslings.com and and tree straps from arrowheadequipment.webs.com. Their prices are reasonable and they ship quickly.
Now my hammock NEVER moves. I can sling it a few inches off the ground if I want with no fear.