When preparing your belongings for moving and subsequent storage, pack them as if you're planning for them to be stored long-term. Put together an inventory, and number and label your boxes on all six sides, if possible. Be generous with your use of tape, too.
When preparing for a move, don't be afraid to telephone shop when looking for a moving storage provider. Most will be willing to provide a quote over the phone, especially if you have a good idea of the total square footage of the material that you need to store.