First concern is the wind. Make sure your setup considers wind direction. Of course take care of your scent.

Then concealment. You want something in from of you and behind you. Camo is important, and consider mixing patterns for your shirt and pants.
Make sure you have room to maneuver your gun/bow.

Then, don't move. Make sure you are confortable. Keep any movements slow.

You leave more scent behind when hunting on the ground, so vary your setups moreso than if hunting from trees.