Pallets, pallets, pallets: Keeping your items off the floor is almost essential. It might sound silly, but there's no way to promise that the melting snow won't come under the door, or the adjacent unit won't have a spill that soaks its way into your heirloom sofa.
Wrap what you can: Using industrial plastic wrap is a great way to know that belongings are sealed up tight and they won't collect dust or creepy crawlies while in storage. Buy a large roll and wrap as much as you can!
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—including the hidden and the obvious. You can even go as far as to make a diagram detaling your items locations (back right corner under the desk = cameras to sell on eBay).
Plan for temperature changes: There are things that don't like the cold or the heat and should either be double wrapped, well insulated or not stored at all. Electronics, vinyl records, old photos (if humid), and things of that nature all come out a little less awesome when not stored properly.
Protect the space: While you're concerned about protecting what you put in the unit, protecting the unit itself is also important — there can be heavy fines for scarring the unit during your tenancy. If you rent one to use for, say, your freelance furniture flipping or restoration business, make sure to plastic off the walls and floors to catch glue drips and sprays (don’t risk accidentally spray painting an inside wall).
Bust out your Tetris skills: Even the smallest storage unit can hold a great deal. 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 you're stacking it up, up and up! It will take the pressure off the tops of your boxes and help keep things safe.
Reprinted with permission - ApartmentTherapy.com