I am having great difficulty using my dressage whip with accuracy. When I go to use it, I tend to either accidentally pull my horse's head in the direction of the whip or miss tapping him entirely. I would appreciate any advice anyone can offer.
The dressage whip -- actually any whip -- should be a quick twist of the wrist. The end of the dressage whip should land just behind your heel, which is why they are so long and is to reinforce the aid that the horse isn't listening to at that moment.
So when you carry your whip, it should lie across your thigh, downwards, pointing from your wrist which is just above the withers towards the horse's rear hoof.
To tap with the whip, your hand should twist longitudinally.
Practise by holding your hand right out in front of you as you read this, and lightly clench your fist as if you were holding the whip. Put a pen in your hand if that helps. The back of your hand should slope downwards about 30 degrees from vertical, thumb straight and on top. Now, rotate your arm slowly so your hand stays in the same place, turning on the axis of your forearm.
Doing this quickly will give you a sharp tap just behind your heel, but, as you have not moved your hand in any direction relative so, say, the keyboard or this screen, you will not be pulling on the rein.
When you do this quickly, you will tap your own thigh. The flexible whip will then bend around your thigh and give your horse a sharp tap with the end.
Be judicious in this, though, it should be your final measure for when the horse has ignored your most gentle aids, your firmer pressing against the flank, and finally the pressure of a spur.