I can't really help with the decluttering as I can't stand mess - it fries my brain and drags me down, so I haven't really ever built up any clutter.
I'm not super organised though and am well aware of my own weaknesses - spending hours filing paperwork into different household catergories would drive me as insane as looking as at a pile of dirty washing.
So I have to strike a balance - where I create a home I can bear to live in without spending hours everyday organising and cleaning it. Not easy when you have dc.
I've worked out what works best for me. I'm ruthless with crap, if its rubbish it goes. The kids have one draw in their bedrooms where they can keep their crap, thats it. I sort clothes out as soon as they outgrow it. I have a big bag for life in the bottom of dd1's wardrobe (labelled with the size of the clothes being put in it), as soon as it doesn't fit dd1, it goes into the bag. When the bag is full, it goes into the loft. When dd2 reaches that size, I just have to pull the correct sized bag(s) out of the loft. No need to spend hours sorting clothes. I do the same with dd2's clothes which will be passed onto dd3. And when dd3 has outgrown them I will take each bag to the local clothes recycling bin instead of putting in the loft.
When bills/paperwork come through the letterbox I sort straight away. No leaving lying around for weeks. If it needs dealing with then it goes into a file tray which sits on the kitchen side. I clear this tray once a week and do everything that needs doing. The stuff I need to keep goes into one meduim sized box kept inside a cupboard upstairs. I dont file anything - I 've worked out that the hours I spend filing far outweighed the length of time it took to sort through the box on the occasions I needed to find the home insurance documents for example. When the box is full, I go through and clear it out, throwing away old documents etc. Takes an hour maxonce a year, sat in front of the TV with a glass of wine.
I have one box of 'keepsafe' things which I have easy access to, so I can chuck things straight in there that I want to keep( things the dc have made etc) When it gets full, its gets labelled and put in the loft. No need to sort or go through.
I dont use a paper diary. I use the calender on my smartphone which is synced with dh's. Every little thing goes onto this calender. I also keep 'to do lists' on my phone so I dont end up with a thousand scraps of paper lying around.
Both the dc know the rountines. We come indoors and coats, shoes, hats, scarves are put away straight away. In the same place everyday. I refuse to spend hours hunting for things. Everything has a place.
They do not go to sleep in an untidy bedroom. While the bath is running they tidy up the mess they have made that day. Every morning before they get dressed they make their beds (I obv help 3yo dd2).
I've worked out that I do better if I get my arse in gear and do things first thing, rather than waiting till after the school run. So in the morning, I put a load of washing on ( loaded into machine the night before), unload the dishwasher, quick clean of the bathroom (normally while the dc are making beds and getting dressed). This means that when we come down in the mornings, upstairs is tidy, even the bathroom. Unloading the dishwasher means the kitchen stays tidy all day as dirty stuff goes straight in.
I'll stop now as I'm rambling too much 