Obviously the most important thing is to purge and pare down. A tip for purging, if you're having a hard time letting go of stuff. For the stuff you really are having a hard time letting go of, put it into a box and put it in a closet or garage or whereever. Set a date - write it on the box. Whatever you HAVEN'T gotten out of the box & didn't need, give it all away on that date. That sort of makes you prove to yourself you don't need those items. It's better if you can just get rid of it right away, but for things you are saying, "But I might use it" - well, prove it.
For me, posting stuff free on Facebook sale groups gets it gone much faster than taking it to Goodwill which is a bit of a drive. I do sell stuff, although some people will advise you not to because it stays in your house longer. For me, I have one "for sale" box and everything stays contained there. The free stuff on Facebook gets snapped up every time, and I just put it on my porch and someone disappears with it. I've even done it where I had a box of stuff (decent, but some was less desirable than others), and I said it was free but the person had to take it ALL.
Make a rule for yourself about buying non-need things. Maybe you need to wait 48 hours? a week? a day? between when you look at it and when you buy it. That will help reduce the amount of stuff coming into your house.
I personally do best working in 15 minute increments for clearing out areas. Trying to power through for hours just exhausts me and I get less done in the course of a day because I burn out, where working in 15 minutes on/15 minutes break makes me work hard against the clock and really energizes me.
Now, this is a bit dangerous, but I do prefer it - in every house, I sort of designated one "doom room" and tackled that last. I got everything else tidied up/purged, and that one room was the last thing, it was where all the random, harder boxes went. Don't do that if you won't tackle the doom room, but for me I really liked getting 90% of the house done quickly.
Every night, do a sweep through the house and "reset" it. Readjust the couch pillows, pick up any books/magazines/toys/other stuff that has been laid down somewhere and put it away. If you do it every night, it will probably take less than 15 minutes.
Identify spots where stuff gathers and make a place for it. For example, my husband IS going to set stuff on the dryer right when he walks in and then again on the kitchen counter. There is no changing that behavior. What I did was put a small basket on top of the dryer and a little pedestal dish on the counter that looks pretty and decorative. I asked him to please put anything he wanted to leave around in those two spots. It looks totally tidy... and his random receipts, screws, small tools, papers all are contained. Plus, if he does leave something out, I can put it into the bin and he knows exactly where to look for stuff, it isn't like I "moved" it on him. If this sounds a little controlling, it is just how I wrote it. Before I placed the "hot spot containers," I asked him if he was okay with that plan, if that would work for him, if he wanted them somewhere else. He was on board, he just wouldn't have taken the initiative himself. It is MUCH easier to change your environment to accommodate than to change someone's behaviors long-term.
Another example - my DH is GOING to leave his shoes by the door when he comes in. It is happening. He (very graciously) asked me where I wanted them to go by the door. Well, I don't really want them to go by the door, but I need to be practical. I created a little shoe area in a corner of our living room with a bench (that shoes fit under - key!) and a hook rack. It wasn't my first choice in how to arrange the furniture, but otherwise I was going to have random shoes splayed everywhere. This gives him a natural "target" to try and get under the bench. Give natural boundaries that people will generally adhere to without you having to nag - for example, I want to put a rug under that bench because if there is a rug, he will put them on the rug completely. Right now he kind of kicks them halfway under. It's the same principle as the bin for his stuff.
Get as much off your counters as you practically can. Get your paper towels mounted under a cabinet if they aren't. It's okay to have some small appliances out, but limit it. In bathrooms, get a small basket or tray and everything that stays out on the counters needs to be within that tray. I position it to DH that it makes it much easier for me to clean (TRUE), but basically - if he is cluttered within the tray, it still looks much nicer than all that stuff being spread all over the counter.
Keep your sink clear. This is so Flylady, but whatever. Keep your dishwasher unloaded (if you have one) and put dirty dishes directly in there. If you don't, wash dishes every time you eat. Dishes in the sink and an unmade bed are the broken windows that lead to my clutter downfall. Oh yeah, make your bed daily. It makes everything look less cluttered.
Figure out where paper comes into your home and put recycle/waste/shredders there. Even if you need to buy another shredder, if paper comes in both the front and back door, get some shredding stations going. We had one in our garage at our last house. Paper coming in and laying around is the kiss of death. Try and switch as many of your bills to auto-pay/e-bill as possible. You can also go
opt out of new credit card offers here. That will cut down on paper coming into your house.
I think that's enough for now, but I'll try to think of others throughout the day.