Stop the horse in an area where you have a visible line in front of you (like a fence, but a good several feet in front of you, or a pole on the ground) this gives you an easy reference point to tell if you are moving forward or back. When asking the horse to move directly sideways, or move the hip, I apply the leg, either in its natural position, just behind the cinch to move directly sideways, or farther back (near the rear cinch if western) to move the hip, at the same time, I lightly lift the rein on the same side, keeping the off side rein steady, but open, away from the body. If I get no response at all (no shifting of feet, nothing), I use my dressage whip to lightly and repeatedly tap just behind my leg until I get a response, while keeping the leg pressure on. With a horse who has learned to yield to pressure, the horse will almost invariably move away from the pressure. Repeat this until the horse moves away from the leg before the dressage whip begins to tap. Then do the other side. Make sure to release all pressure (whip, leg, and rein) as soon as the horse moves away from the pressure. Once the horse begins to understand the concept, keep the leg pressure on for two or three steps, reapplying taps with the whip if the horse stops after the first step. What you're wanting to accomplish is for the horse to keep moving as long as the leg pressure is present.
When wanting to move the shoulder, I do exactly the same, only use the dressage whip just ahead of the leg, actually on the shoulder, but not so far forward that you're swinging it anywhere near their face, you don't want to spook them into moving, just pressure them into it. This usually accomplishes the goal very quickly.
It doesn't do much good to demand if the horse has no idea what you're demanding! :)