Use pallets, 2 x 4's, plywood, any thing that will keep your items off the floor of the unit.
Utilize all the space in your unit. Make a plan as to how you are going to arrange your items. A good plan will save you the time of having to rearrange your unit. Leave an aisle in the center of your unit so that you have a walk way to the back of the unit.
Use freestanding shelves to help organize your unit.
Label the boxes on all six sides and keep a list for easy reference. This will save you time if you have to look for something in particular. When packing boxes fill them without making them too heavy to lift. Always put the heavier boxes on the bottom and the lighter ones on top of the heavier ones. This will prevent boxes from being crushed. Keep boxes off the floor.
Be sure to store frequently used items at the front of the unit to avoid having to search for them.
To protect your items cover them with moving pads, sheets, or light blankets.
Be sure to check your unit once a month.
Disassemble items such as tables, bed frames, etc. (This will save space.) Wrap and label all pieces for an easier time when you have to reassemble them. Put all hard ware in bags and mark the bags accordingly.