If you want to rent a self-storage unit, then you will need to decide what kind of facility and container you want to use. Here are some features that you might want to keep an eye out for:
You should determine whether or not you need climate control in your storage unit since this will narrow down your options considerably. You should also take a look at how expensive climate control is in your area. If you live somewhere that is very cold or very warm, climate control will generally be much more expensive than you might find in a temperate area.
If you do live somewhere that has good temperatures year-round, you might be tempted to skip climate control entirely. However, this isn't always the best idea. Aside from the temperature, you need to keep an eye on humidity. High humidity is particularly dangerous to electronics, wood, paper products (like books), and leather products (like some furniture). It can lead to degradation of those items fairly quickly.
You might think that you only need a unit with climate control if you want to keep your stuff refrigerated, but that isn't exactly true. If you live in an area that has extreme temperatures in either direction, the majority of your belongings could suffer damage in a unit that lacks climate control. Although these units do have some insulation, the temperature inside and outside will likely become fairly similar over a long period of time. Too much heat could lead to certain products melting. Too much cold weather could result in ice forming on your stuff, which can cause problems with electronics, paper, and leather.
You'll also want to consider how much security the facility has. In short, you will need to figure out exactly how hard it would be for someone to break into your storage unit and damage or steal your belongings. Some storage facilities require identification to even enter the facility grounds while others might only have security measures on individual units. Some have security cameras that cover the entire facility while others might have blind spots.
Ideally, you want to find a facility that has 24/7 camera coverage on the specific unit that you want to rent, as well as security measures that are proportional to the value of your belongings. If you are storing a lot of valuable stuff, then you probably want a security system that is a bit more complicated than a simple lock and key. An electronic keypad in conjunction with a padlock is a good start, but you might even want to find a facility with a fingerprint scanner if you feel that your storage unit needs that much protection.