The 501st
Rex sleeps on his back. His head and shoulders are always propped up a little bit, no matter where he is - in the field, he usually ends up sleeping sitting up. More often than not, one foot is braced against the mattress - or the ground - so his knee is pointed towards the ceiling, ready to spring him into action if necessary. When inside, he always positions himself closest to the door, always facing it, ready to intercept anything that came through it. When he and his men don't have the luxury of four walls and a roof, he makes a habit of camping on the edges, a one-man buffer between his men and the droids.
Ahsoka sleeps on her side, curled up like a cat - or a waiting nexu. She always uses her hands as a pillow, tucking them neatly beneath her head so her cheek rests against the back of one hand. Her knees are always drawn up towards her chest, toes pointed down - how tightly they're pulled in depends on where she is. In the safety of the Jedi Temple, her knees are barely bent, but in a warzone camp, she curls in on herself so tightly that Anakin is constantly surprised her spine isn't broken - or at least seriously distorted. She takes the high ground when she can, preferring the top bunk or the overhanging ledge. She tries to take a central space - or near to it - in an attempt to reassure herself, when she wakes, that she is not alone in this war.
Very few people have ever seen Anakin sleep. Most of those who have only saw him unconscious after his latest escapade. The Hero With No Fear sleeps rarely, and never for long. He is too busy patrolling, pacing, caring, to worry about things like sleep. On those rare occasions he does sleep, he sleeps on his back, staring up at the ceiling - he's never been able to sleep outdoors, he's always too paranoid that something will sneak up in the dark and steal someone away - until he finally gathers up the courage to drift away. Since the war started, he hasn't slept more than four hours at a time. Usually, he sleeps less than two. He can never quash the feeling that something will go wrong if he's asleep for too long.