While some people need a place to store their belongings for one month during a move, others require long-term storage solutions. You may be tempted to find the smallest unit and stuff it to the brim, but making a plan for space usage will pay off in the long run.
Consider how often you will need to access your items. During the packing process, label each box clearly. As you unpack things into your storage unit, put the items you use the least often in the back. You might even want to consider renting a storage unit big enough to enable you to walk through to the back, to give you easier access.
Whatever the case, you will be able to enjoy 24-hour access and a fully lit, secure area when you visit.