Your gun should be in your hands, not slung on your shoulder. Some guys carry with one hand, some with 2 in a "ready" position. Just get used to the motion required to bring the gun to your shoulder and get the sights aligned. Practice it with the clothes you will be wearing while hunting.

Any handy gun will be fine for still hunting. Scope should be set on the lowest power possible. If you have a fast pointing 12 ga, by all means use it.