Focus on maximizing empty horizontal surface space.
Explanation
Have you ever noticed that restaurants and bars often decorate their walls with stuff that would easily be considered clutter on the floor?
Apparently “clutter” is a highly relative descriptor, and the visual-spatial bias behind it privileges horizontal surface space.
You can leverage that knowledge to quickly de-clutter spaces without investing in lots of new storage furniture and organization systems.
It’s by far the cheapest trick I know.
How (basic)
Move and reorient items from horizontal surfaces to vertical ones.
Horizontal surfaces include table tops, floors, chair seats, and so forth.
Vertical surfaces are everything else: shelves, hanging storage, stackable cubes, upright bins, baskets that can sit on top of cabinets, boxes that slide under beds, wall-mounted anything, shelving beneath any horizontal surface, any storage above eye level, etc.
Even just stacking things can make a space look less cluttered.
How (advanced)
Once you start getting creative with this concept, you can build it into the planning of your living space.
For example, you might figure out what stuff can live in wall-mounted dispensers instead of occupying the space of a counter/vanity/floor.
Similarly, you might find visually appealing ways to store “clutter” out in the open, such as a ceiling-mounted pot rack or a stainless steel prep table used as kitchen island storage.
One of my favorite side-effects of this technique is that once you’ve minimized the footprint of items lying on horizontal surfaces, cleaning becomes a snap.
For example, fewer obstructions on the floor lets you use cheap sweeper bots on a schedule that keep interior dust levels low.
Likewise, wiping off counter tops and bathroom vanities takes mere seconds when you don’t have to move anything.
ETA: tldr — “picking up,” interpreted literally, is an endlessly useful principle of housekeeping.