I've found that the #1 strategy in preventing hairballs for my cats is to feed a diet very low in dry food.  Secondly, fish oil between meals helps get any hair in the stomach moving through the digestive tract.  Eliminate corn from the diet completely, as it is not digestible to the cat and can get caught up with the hair in the stomach.  Other non-meat substances should be eliminated if possible, but corn is the largest problem.  I hope this is helpful.

Vida.