Your "go forward" cue is extremely important when working on shoulder control with your horse. It should be something like a "kiss" from the ground or a bump with the legs from the saddle. Although using a dressage whip like an extension of your arm to gently tap the horse can be helpful, you will never actually hit him with it. If your horse won't go forward from a "kiss," a leg bump, or a whip tap, go back and refresh this basic training.
Spurs do have a place in the arsenal of highly skilled horsemen, but they're often used incorrectly by less experienced riders.
Here are some reminders:
1. Spurs are NEVER used to cue a horse. They are only used to let the horse know he has missed a cue.
2. Unless you have excellent control of your leg position, you might not want to wear spurs at all. If your horse makes an unexpected move and you instinctively "grab" with your legs to stay on, you could easily end up spurring him forward when what you really want him to do is stop.
3. Never use spurs on a green horse. Give him time to learn the proper leg cues.
4. If you put spurs on, you are more likely to use them.
5. To keep your horse fresh to spurs, don't wear them very often.
6. If you must wear spurs, use the mildest ones you can find. Some are just blunt knobs. Or, you can cover rowels with duct tape at first to get your horse used to them. It may not be stylish, but it's a smarter way to start out.