I have always had trouble spotting. One teacher gave me this exercise. Stand in front of a mirror (at home a bathroom mirror is good) and stare at your face. Start a march, and move your body into a turn, but keep your eyes on you in the mirror. Keep turning the body around until you can't keep that stare, then whip your head around to catch the same facial image in the mirror. Continue to repeat, then work the opposite direction.
Remember to keep your body up and centered. Try to keep your head in the same position in the mirror, not moving from the starting point. If you need to, draw a head-place (upside-down "U") on the mirror with a grease pencil, so everytime you turn your head the head and face land in the same place.
The circular march can be slow or fast. Work slowly at first to position your head in the same place in the mirror.
The key, in my humble opinion, to spotting is to make sure the head does minimal movement when "whipping" around. If it whips to an off-side place each time, then the stuff in those ear canals moves to a different place from which it started and has to adjust in the canals, causing dizziness. Think of keeping your head in the same orientation as you move. The head should be stable.
I hope that makes sense.
balletboy[/i]