Apart from getting rid of stuff, just don't bring stuff into the house. Don't impulse buy. Birthdays and Christmas I ask for consumables (like gin, or nice cooking oils or something) or book tokens or restaurant vouchers etc. If I get bought a toiletries set that I'll never use (I have sensitive skin) then I don't keep it lying around the house for a year or two thinking "Oh well maybe I'll just use the hand lotion out of it". Instead, I just give the whole set to charity straight away and don't feel guilty about it. I don't like receiving stuff off people really. I have everything I need and buy stuff I don't have as I need it if it's essential. So, things like hand cream I buy as I run out of it which isn't very often so if I run out in October, I don't want wait until Christmas so that someone can buy some as a present. Stuff for the house I want to choose for myself, I don't want someone else's taste in decor foisted on me. Even scented candles etc are a personal thing. Jewellery, I have plenty of, I really don't need any more.
This is the problem - we are a consumer culture in the West. Our economy is built round constantly buying things. Which means "things" are brought into the house all the time. This didn't happy years ago. You kept stuff till it wore out. There were no silly things like Christmas Eve boxes, or massive piles of presents on Christmas Day either. No piles of Easter eggs in plastic on Easter Sunday. Too much STUFF!
So that's my advice. Just cut back. Don't buy stuff at all unless you absolutely need it. Otherwise you'll declutter and get despondent as stuff just seems to accumulate.
Be ruthless with books. Old recipe books which you use for just 2 or 3 recipes, take photocopies or scan or write in a "Favourite recipes" notebook. Don't keep every book you buy, there is no need. Or get a kindle instead!
I took a few days to declutter my teenaged son's bedroom. We were really ruthless. There were lots of box games that they rarely played with, or craft sets they weren't bothered about. We sorted the lego sets into the correct boxes, put most away (for grandkids maybe, as I couldn't be arsed ebaying!), and only put a few of his larger Technic vehicles out on display. All the books he'd kept in case his younger brother wanted to read them were giving to charity (sadly his younger brother is not a reader
) so I conceded defeat and sent them somewhere they'd get some use. He just kept a couple of old faves like Harry Potter etc.
His shelves which previously had been packed full actually had room to put his things on nicely, a couple of display items. It looks so much nicer, calmer, and is very easy to tidy and dust now. It's the best decluttered, tidy room in the house now and I need to do every other room in the same way as it will save so miuch time cleaning and tidying.