SlowButSteady, I have had similar issues with clutter. I'm a pack rat by nature and tend to accumulate stuff and it doesn't help that I'm a procrastinator too. I'm still working on my clutter demon but I've gotten so much better.
Here are the steps that worked for me:
1) Identify most common clutter traps. Find a system to deal with those, like sorting the mail over the recycle bin that someone else suggested, so that you don't add to the existing clutter. For me it helped to ask my neat freak friends about their habits and observe them in their homes.
2) Restrict what comes into the house. This may be hard to do since you're not the only one who's responsible for the clutter. And you've already mentioned that the other members of the family are resistant. You can't force anyone else around you into change but you can work to change yourself. Let them keep their man cave to do what they want with it. It's the one room that you don't get to criticize. Just ask them to keep the door shut to it and respect that you are trying to get the other parts of the house clean and to please not clutter out there anymore. Someone already mentioned that before you bring in anything into the house that you have to get rid of something first. That is a great idea. However for the clutter situation that you described, you might want to start with letting go of three things for every one item that comes in. Once you're into the maintenance stage you can do go down to 1:1.
3) In the beginning, work in 1' x 1' sections. It is overwhelming to take that kind of clutter as a whole, so work in small sections. As you get better you can work in larger sections. It helped me to lay down something that I could use as a border for the section I was working in, like an embroidery hoop or a small box with the top and bottom cut out. Sort the items by keep, throw out, and giveaway/sell. It helps if you have bags or boxes at hand while you sort. When you're done, you have to find a home for all the items that you've decided are staying. It was very difficult for me to do this in the beginning. My natural inclination was to put many of these items in a new pile in another part of the room, so the piles where just moving around. Ug! Sometimes the part of the house the items belonged is was so cluttered that there was no space to put them into without cleaning out that first. If that's the case put them into a box or bag and keep them in a place where you can easily pull them out once you're ready to organize that space. Plastic see through bins are nice because you can view the contents, but the cost of those can add up quickly if you need a lot of those. I used a lot of paper grocery bags since they can stand up by themselves and I could write down what was inside. Keep a container for each room or category of items. Keep like with like. It's so much easier to see if you have multiples of the same thing. I also kept a box for those items that belonged to Dh that was placed outside his explosion room and asked him to put those items away. If they stayed in the box over a week than I assumed that it was alright to throw out. I felt like that was a reasonable amount of time for him to either take care of it or pull the items into his man cave. I did make exceptions for the things I knew he would miss eventually and placed them into his space. That way it was on him if he couldn't find them: "I placed it on your desk, honey. What happened to it after that, I do not know." He never missed the items I threw out. He probably forgot he even owned them.

4) Or for a small space, such as a bathroom or linen closet , pull everything outside onto the lawn. And only bring back things you need or want to keep. For the items that are not a necessity, ask yourself when was the last time you used it. If it's more than a year or two then reconsider your decision to keep it. If you can't get yourself to part with some of those thing, put it into a box dated six months in advance. If you haven't used those items in that time, then chances are you don't need it. Get rid of it.
5) Before starting a new section, maintain the section you've worked on first. It takes getting used to but it's so much easier to do maintenance once an area is clutter-free.
Remember that it's easier to replace a bad habit with a good one than to break yourself from a bad habit cold turkey. If you find yourself feeling guilty or playing the shoulda, coulda, woulda mind game with yourself, that is the time to just do the thing that's on your mind instead of beating yourself up about falling into old habits. Another thing I do is to watch shows about dealing with clutter. They show homes that are way worse them mine which makes me feel a bit better about my mess. And are a reminder of what could happen if I let things go too far. I pick up tips in the process. My favorite is How Clean Is Your House produced by BBC. I don't watch it often, but every time I do, it makes me want to scrub down all the surfaces in my home.
Everything in moderation, including moderation.
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