The biggest thing is to make sure that the garments are clean before you store them, because dirty wool (esp. with food stains, etc.) attracts moths. Anything with a strong odor (cedar blocks, lavender, bay leaves) will help deter moths, but isn't fool-proof. The only thing that kills them is a high concentration of mothballs in an airtight container.

Some people wrap the items in brown paper or put them in cotton pillowcases (moths prefer protein fibers but will eat both paper and cotton if they're really hungry). I have also heard of people using dry ice to create an oxygen-free environment in which to store wool, and using a microwave to kill moths that are already present. Storing in a hermetically sealed container or vacuum sealed plastic bag also helps deter them, and keeps the infestation contained if one of the bags had moth eggs in it before it was sealed.

If you are really worried about it and can stand the smell, the best strategy would be to put them in mothballs.