Use a sling. I can shoot without one, but feel much better about it when I have one on the bow, especially in a treestand.

One little thing I picked up from a buddy that really seems to have helped me. When gripping the handle, place the tips of your fingers lightly against the front of the grip. The concept is that if you do happen to squeeze the grip a little, the it wont actually twist the grip, thus torquing the handle. I've been shooting like this for a while now and really noticed that my left/right shots have been minimized quite a bit. This may or may not be "politically correct", but it seems to work for me.