Plan before you start loading your unit - make sure items you will (or may) need are towards the front and reasonably accessible
Leave an isle in the center of the unit in order to access items you have stored in the rear
Use sturdy plastic containers for small items - cardboard boxes do not stack well or work well for storage.
Do not store any dangerous materials, perishables or food items.
Store small items in bureau draws and similar available spaces.
Store mattresses, couch cushions and similar items on pallets to allow adequate air circulation.