Can you prioritise rooms - eg kitchen, bathroom? Where there is likely to be less emotional attachment to stuff? Start with out of date food and multiple items of equipment.
Or prioritise safety - so get rid of stuff on the stairs, blocking escape routes etc.
Things for charity shop/rubbish get out of the house straight away.
Arm yourself with cleaning products, bin bags etc.
Don't try and do too much in one go. overwhelm is a thing.
Leave the potentially sentimental things for towards the end.
Is there a goal at the end - eg do they want a clear, calm sitting room.
My favourite follows on Instagram for this sort of thing are:
- Orjenise Based in Leeds has a lived in looking home - is not minimalist! Has some lovely baby step type declutters.
- theorganisedmum Systematic, doesn't like cleaning, has clutter buster programmes/bootcamp. Suggests going into a room and sorting in one direction rather than flitting from place to place
- declutterdollies Dily from sort your life out, plus some of her Dollies. She's scary. She was very poorly a few years ago and her tips on organising for her after care at home were (I thought) spot on. Systemise is her catchphrase . She seems to be a big fan of matching storage boxes, which is lovely, but potentially expensive!.
I'm also a big fan of the 'Sunday Basket' - which is a system where you basically stick everything paperworky in a 'basket' and sort out once a week, with the todo into labelled folders which are in the basket.. So it allows forward planning - I used it loads when my children were at school and I needed to plan for school trips, assemblies and events, but you can use it for anything 'life' orientated - so hospital appointment letters, bills, etc. I just used a basket from B&M big enough to take A4 paper and then some cheap dividers with labels on - mine currently say. Business, Work, Bank, Council, Car, Hobby, and Health, but they do periodically change.