Less stuff and then planning the storage to organise the stuff that you keep very well. We put storage racks in cupboards and having containers that fit those racks perfectly meant that not an inch of space is wasted.
IKEA was our friend!!
We put IKEA IVAR under the stairs and the Samla clear box range fits those perfectly along with the IVAR metal drawers and basket shelving.
We also put ELVARI racks and shelves into a random L-shaped alcove in the bedroom, and with a door, created a small walk-in wardrobe. Kuggis tubs fit those shelves perfectly - plus they are vented so it worked well for linen storage under the hanging rails. (You might be able to put your vacuum bags in these too)
Shoe storage in the downstairs loo at the front door so no need to store shoes in cupboards upstairs so more space for other things. (Added bonus - clothes don’t smell like trainers!)
We also added second rail to one wardrobe to double the hanging space (shirts and trousers fit so no long stuff unfortunately but it’s not like I’ve got much call for long evening wear at the moment)
We also built a cupboard and bookshelf onto the landing. This had to be a custom build because nothing standard fitted well. Lots of shelves for books and filing. Doors on it so you can’t see what’s inside. We made sure it was just deep enough so that ring binders fit onto the shelves.
Shelving racks in the shed too (IKEA again - just the very cheap racks with the Gles plastic tubs that stack without needing lids)
Kitchen has lots of “clever” bits - pull out racks for the corners etc. We put in two single units, rather than one double unit on the walls so the shelves inside can take more weight without bowing. Pot drawers instead of cupboards seem to use the space better too.
It’s working well for us because everything has its place, but if something is not in its place, it can look untidy quite quickly!!