IMO
Scent control
Treestand cover (will conceal small movements)
Treestand Height (will also conceal small movements)
Movement in stand (if 2 and 3 are good you can actually get away with a fair amount of movement)
Camo (although I own way to much of it if there is ever such a thing)
Smoking (before I quit I've seen plenty of deer while smoking. Some even down wind)

IMO it's best to be between 18-22 feet up a tree. This gets you high enough that you're not obvious to the deer but no so high that you'll be shooting an overly steep angle. I'm a sent control freek and think this can't be overstated. Just stay patient and let the deer move into position and when you are obstructed from their view is the time to make your move.

You might think your bad at this but you've choosen the most difficult(IMO) method of taking a deer. Stick with it becasue the rewards are unmeasureable.