You will want to start with thinking realistically how much stuff you have that you are wanting to store.
Don’t fail to have a plan, be sure you know what you are storing and where you will be storing it. An inventory list could be most helpful, or at least labeling the boxes with what is inside.
Don’t waste space you are paying for. Be sure to disassemble your furniture (beds can be stored vertically). This goes for mattresses also (be sure you have them covered).
You are also going to want to be sure that you have room to access all the items you have stored. You aren’t going to want to jam pack everything in and not be able to access your certain items at any given time. Leaving even the smallest of a walkway may make a world of difference and convenience.
A little bit of planning can save a headache and unnecessary frustration.