I'm often told "I'm overwhelmed, I don't know where to start" by my clients; and it's understandable - without systems in place it's easy for anything to get out of control. I will admit to some OCD-like tendencies, perhaps because of spending so many years living on a submarine and having no room for anything. There were several years where I was hot-racking, sharing 2 racks between 3 people; out of necessity you learn how to pack and bring only what you absolutely need. Add to that my training as a Lean Six Sigma Green belt and it's a wonder I don't have my everything in my house labeled and it's location identified (I don't, I promise : p ). I am NOT a professional organizer, although I do know a few and will gladly recommend them if asked.
When my wife passed away I was overwhelmed by how much she had left behind that I didn't see the value in - they weren't my hobbies or passions; to me it was just "stuff". I didn't want to get rid of anything at first, because it reminded me of her, but it also really stressed me out. So I started by moving anything I was absolutely sure I would never use - like a sewing machine and food mixer - to a corner of the living room. These were eventually sold on Craigslist, several months after I started the process. And (5) years later I still have things of hers that I'll never use, like clothes and knick-knacks; I've kept because they remind me of her; but now they have a place that makes sense to me and I don't feel overwhelmed.
But what about everyone else, where can they start? When you get to the point where you're feeling overwhelmed it's really difficult to overcome inertia - and it can feel like you're not making any progress. So let's begin by addressing what to do before it gets to this point, and many of the same steps can be taken at any time - it's never too late.
For me, the easiest place to begin is getting rid of loose papers. If it's documentation I need to keep - like tax records, my son's IEPs, etc; I scan and digitally back them up. I can always print them again if needed; then it's off to the shredder. Paper can take a LOT of space, and it doesn't take very many loose pages to give the perception of a mess. It's also fragile - susceptible to water damage, tearing, fire - you get the idea. With the availability of the free cloud resources, Google Drive for example, there are plenty of places to back your records up. And documents do not take much memory. This has the added advantage of allowing you to keep things indefinitely. I know many people who don't want to get rid of their documents, just in case.
Next thing to consider is anything you haven't looked at in a while - to start let's say > 1 year. This could be boxes in the attic or basement from when you moved, or even a storage facility you're paying for but haven't been to in a while. I think it's safe to say most of us have something like this. This isn't the holiday ornaments you only break out once/year; it's the items that don't seem to fit in your home now, or things you put into storage a while back because you didn't know what else to do with them.
I'm a financial planner, my career and profession is centered around helping people get the most out of the money they have. In my opinion it's easy for storage facilities to shift from a very useful tool to a money pit - if for no other reason than someone has the wrong size and could be saving themselves a little on the monthly fee. More often it's because people have forgotten what they put in storage. If it's family heirlooms or antiquities you're protecting until your young children are old enough to understand the value, that's one thing. But if it's IKEA furniture bought when you got your first apartment and stuffed into storage after you got married let's look at getting rid of it and invest the money spent on the storage facility towards your future.
The same goes for your house, it's easy to accumulate stuff - especially the longer you live somewhere. So start small, especially if it feels overwhelming. Rather than tackle the entire room, pick a dresser or shelf and work on that. Let yourself see that you CAN have an impact - even if it's just getting rid of clothes you never wear or creating a clear space on the shelf. Take small steps if this is uncomfortable. Bag clothes up and put them in the closet or somewhere out of sight, then in 2 - 3 weeks if you haven't missed them, drop them off at a charity thrift store or call for a pick-up (tax deduction).
No, this isn't going to make you rich; but that's not the intent. It's one less thing you need to think about, it's going to free up some bandwidth. We all can only fit so much into our brains, and then something has to give. And it's important to understand this isn't an overnight solution, it's not meant to be. For some of us it could take months or years, depending on our circumstances. And I'm not suggesting you live like a monk, if you enjoy a collection of something that is not the same thing as being overwhelmed by clutter. And there are professionals who can help - not just empty a house, but creating better habits and understanding why you feel the way you do. At the end of the day it's a question of your comfort, no-one else.