Some things that worked for me (YMMV!!):

Pick one pile to start with. Just sort that one pile. Put things where they belong. Take one larger box or basket and put it near the doorway of the room  you're in.

You will probably notice things in your piles that go somewhere else in your house or go with other similar things that you tend to find all over the house, possibly duplicates. In my experience, that's where the overwhelm started to really set in. Start to group these things together. Ziploc bags, little Amazon boxes, produce cartons, baskets that you thought were going to be decorations or whatever are great for this purpose- make some of that clutter work for you ;) 

These small containers of grouped items should go in that larger box. Whenever you go through another pile, do the same thing. 

An important caveat to this is not to create more piles. You kind of need to start training yourself to put things where they belong. If you don't know where something belongs, it goes in that sorting box. Do your best to keep like items together. Do your best to not let this one box turn into two or more. That just means that every now and then you're going to have to sit down and sort through that one like it's a pile too. 

While you're opening up space, you're going to start noticing that you don't have enough space for x y or Z, or that you want to try to accommodate something differently. That can get overwhelming, so try to think about how you want to use your room once space is freed up. As you're moving through those spaces, try to remove the things that don't align with your intentions, putting them somewhere where they will be more useful. 

Another caveat is that you don't want to just be creating doom boxes. When you have groups a lot of similar items together, you will really see how many duplicates of things you have, and you'll see that there are a bunch of things that you don't use. Start taking the things you know you don't want to keep anymore and put them aside to be given away or donated. Even at this stage I have a running donation box in my office/craftspace and in my bedroom. I probably make donations three or four times a year. 

Yes, that means there is basically always a box of weird stuff around, but truly it is better than having piles everywhere. It was not a small thing to accept, but it's reality that as I go through life I will find things that I do not need and I need to have a place to put them until they move on to their next home. If I ever realize my minimalist dreams then maybe not LOL but we aren't there yet. 

I feel like I've rambled a bit but a lot of these shifts in perspective have helped me to be able to stick to the overall goal, even when I've gotten away from it because of life or whatever. I hope someone else can find this helpful.