There are a few different types of storage lockers. One is the kind that you can keep at home and is made of metal, wood, or plastic. The other kind of storage locker is the kind you have to drive to and is a large locking storage space where you can keep your things on someone else's property. I like the latter kind, since it has a lot of space and you do not have to look at the things you are storing until you need them.
When organizing this kind of locker, I suggest you put things into smaller boxes. If you have a gigantic box that you fill with books, for example, you may find that lifting that box when it is full is a quite unpleasant task. And once you know a book is in the box, you'll have to dig through a lot of other books just to get to it, at which point in time, you will need to put all the books back in the box, making sure they all fit in the box as they did originally. I suggest you not only make lists of the contents of each box, but also either post those lists on the box or keep the boxes labeled with letters or numbers and keep the master list on your computer at home...or perhaps even both.
What if you are using a different kind of storage locker? The way you organize one of those really depends on the size and type of container, as well as the intended contents. If the locker is a kind of metal cage, you may find that you will need large containers inside it to organize smaller things that could slip out of the locker. If the locker is solid plastic, metal, or wood, you can use smaller containers to break up the things you are storing in your locker. If the things you are storing are too big for that, then that may likely be why you have a storage locker and can therefore rest assured that your storage locker IS the organizing container itself.