As with a lot of tricks, you have to get used to your legs moving in different directions. It's really just a question of mind over matter - but that isn't too helpful.
You could try standing on the ground behind your board and spinning it around just using your back foot. You can see what I'm talking about 45 seconds into the following video:
http://www.youtube.com/watch?v=mQjesMsq_AoOnce you have got that movement nailed you can try it on your board again. Use the same movement with your back foot/leg and try to concentrate on keeping your front foot centred in the middle of your board. It helps if you think of your front foot as a fixed pivot point, which the board rotates around.
Also, if you had any trouble keeping your ollies straight and figured out how to stop yourself from turning, you would use the same technique to avoid spinning during a shuvit.