Use the 'Out in the Open' Technique to Declutter Closets and Drawers
When you have a big mess in your home, you may already use the pile method to fix it: You drag the mess out to the center of the room, then start dismantling it bit by bit. But what about when the mess is contained—as it technically should be—in containers, drawers, closets, and other hidden spots? Using containers to, well, contain your possessions is the best way to stay organized, but that doesn't mean you can't or won't end up with a disaster inside of them. In fact, when everything you own is stashed away, it can be hard to register that it even is a mess, since it all looks so presentable from the outside. Duplicate items and messy container interiors are a scourge, but you can use a modified version of that pile technique to fix it all.
The "out in the open" technique
What you're going to do in this case is something called the "out in the open" rule. It comes courtesy of decluttering gurus The Minimalists, who also came up with the popular "packing party" technique. When you do a packing party, you box up everything you own, then spend three weeks living like you just moved into your home, unpacking only what you need. After three weeks, you're left with boxes of stuff you didn't need access to for 21 days, which likely means you don't really need most of it at all. The Minimalists call "out in the open" the "reverse" packing party because instead of boxing everything up, you're unboxing it and making a big pile of stuff to kick off your decluttering.
Essentially, you pull everything out of where it's stored. Closets, boxes, containers, baskets, drawers, cupboards—it's all fair game. Once everything is out in the open, you're forced to deal with it instead of continuing to ignore it, like you do when it's out of sight. This means you'll end up throwing or donating some and reorganizing the rest.
How to actually use the "out in the open" technique
This is a pretty labor-intensive approach to decluttering—it won't be one of those things you can do in a few minutes. You are, after all, committing to making a giant mess before you even start cleaning. This technique also stands contrary to most of my typical advice because with this, you should try to do larger swaths of your home at once. Usually, I suggest decluttering and cleaning smaller areas, but here, you're going to want to do multiple containers, closets, and storage areas at once.
The reason is that one thing you want to do is look for duplicates of items. If you're following the Organizational Triangle (and you should be), you should be storing similar items together in the same place, but that's the kind of rule that's easy in theory and harder in practice. Are all the scissors in your home in the same drawer? What about all your lip balms? Your tech chargers? Pulling them from different sources and storage locations, getting them all together in the pile, you'll see how many duplicates you have. The pile itself also serves the larger purpose of simply making it visually clear how much volume you have. Seeing the excess stacked up can counteract the hesitancy you may feel to get rid of things "just in case" you need them in the future, might miss them, or think they have a sentimental value. If you struggle with throwing or donating things because of feelings like that, this mess could be the answer.
Once you have everything emptied out into a big pile, use a technique like the 20/20 method to quickly weed through it all. Ask yourself two questions: If I needed this item in the future, could I replace it for under $20? Could I replace it in under 20 minutes? If the answers are yes, get rid of the item. If you have duplicates, get rid of all but one. Once the pile is pared down, place whatever remains back into the storage boxes and areas it all came from, taking care to store similar items together so you know where they are when you need them.