Having a specific, unique spot for everything I own has made my life much better.
My desk tends to get cluttered, same with closet and bookshelves. (Half-price books is secretly my organizational nemesis) Horizontal surfaces especially tend to end up being “catch alls”, and quickly fill up with a variety of things, making them both un-usable as surfaces, and very poor storage options as you don’t know whats actually there.
So create a space for everything! This idea is obviously not mine, it exists in a variety of sources very old to quite new, but it has been great.
It can be hard, but there’s a couple tricks. If something doesn’t go anywhere obvious, do some honest, deliberate consideration as to whether you need it at all. If you don’t, get rid of it; if you do need it, make a place. Shelving and other organizational tools are available in every form you can imagine. They’re inexpensive if you’re patient and shop deals, free if you troll craigslist and other free sites.
The second: have places for consistent, temporary objects, like mail and empty amazon boxes.
If you’ve having trouble, ask a friend for help! Most friends will gladly help you bounce ideas around, help you come to terms with parting with nostalgic nick-nacks (or find them a good place), and move furniture.
Finally, when you find something new or unaccounted for in your “first sweep”, make a new place for it.
Its a fair amount of work to start, but it pays itself back in time, happiness, reduced stress, and easier to exist in living spaces extremely quickly.
Walking into my garage makes me happy; the available space, the access to everything I want.