Homes in the UK are the smallest in Europe on average. There are thousands of sources online with storage solutions and room layouts that assume you’ve got space to give up.
Most people start with storage (although it’s usually the wrong place to start). It’s easy to rush out and buy a new set of boxes or storage containers. But it’s worth first determining what’s taking up all the space. It’s not always clutter.
Natural light and the placement of mirrors (especially rooflights) are great for improving the perception of small spaces.
There are better storage solutions than under stair cupboards. A lot of small homes leave under stair space as dead space when it could be a desk or some drawers.
Bi-Fold doors can be great for opening a small living room onto the garden, but if the space is too small to accommodate the full opening of the doors, then you end up with a room you can’t use because it’s blocked off.