Decluttering storage spaces can be different from decluttering rooms like the kitchen, your closet, the living room. Where the stuff in rooms usually falls into a few categories, storage spaces hold a smorgasbord of items that may have little in common … beyond being things that have no to little use in your life.
Unless you have many hours, a lot of space, and high energy (and patience), you might not want to sort everything in storage into categories. This means opening and sorting through the contents of individual boxes (which is perfect for working in short bursts).
If you’re keeping the items, make certain the outsides of the boxes are labeled. You can then organize the boxes or bins of stuff that you’re keeping by category (Christmas decorations, camping equipment, tools, etc.).