GET INSURANCE. Check the web for different companies. There are several.
1. Pallets, Pallets, Pallets: Keeping your items off the floor is almost essential. Concrete is not water-proof. All items that are stored directly on concrete are subject to moisture from the concrete. After heavy rains this is especially true. Also, there is no way to promise that the adjacent unit won't have a spill that soaks its way into your stored items.
2. Wrap What You Can : Each time we use a storage unit, we wrap what we can in industrial plastic wrap. That way, we know that things are sealed up tight and it won't collect dust or creepy crawlies while it's doing time. Check out Ulinefor easy ordering of large rolls.
3. Use A Hefty Lock. Vallejo self storage requires that 2 high quality disk type locks be used on each door to make it harder for burglars to brake in.
4. Label, Label, Label: Even though you know exactly what you're putting in your storage unit at the time you open it, that doesn't mean in 6 months when you need back in it that you won't be digging for ages and opening random boxes until you find what you're after. Label everything. The hidden, the obvious, and you can even go as far as to make a checklist that hangs inside the door telling you where something might be (back right corner under the desk = cameras to sell on eBay).
5. Plan For Temperature Changes: Although this might not be an issue in some parts of the country, there are a few things that don't like the cold or the heat and should either be double wrapped or well insulated or not stored at all. Electronics, vinyl records, old photos (if humid), things of that nature all come out a little less awesome when not stored properly.
6. Bust Out Your Tetris Skills: Even the smallest storage unit can hold a great deal, just make sure you use the space wisely which means packing things all the way to the ceiling. Bringing in plywood to lay across several boxes can help stabilize layers as your stacking it up, up and up! It will take the pressure off the tops of your boxes and help keep things safe.
7. Don't store anything that might be ruined by humidity! Self storage units are prone to having water get in the floor and in the air; these are not climate controlled units so you must not store something that is sensitive to mold, mildew, or moisture in the air.