I adopted the motto of "a place for everything and everything in it;s place" and trained myself to put things back in the "right" place after every use, whether it be a particular pocket in my jacket, or a particular compartment in the handbag, or hooks in the house (for keys), hanging coats/jackets in the cupboard when I come in, along with shoes in the hallway shoe rack. If you do it enough times, it becomes habitual/second nature.
For household/stationery items, it's the same really, scissors live in a particular drawer with batteries, lightbulbs, small took kit etc. Stationery is in some organiser drawers, envelopes in one, notelets/paper in another, spare "open" greetings cards in another. Tippex, pens, pencils, ruler, etc in their own drawer. After literally months/years of forcing myself to put stuff back where it belongs, I now find I don't lose anything anymore. Beforehand, I'd just put stuff randomly somewhere, or leave it where I used it, and of course, it'd take forever to find again.
For clothes, I have a couple of chests of drawers, so plenty of space to spread out all my clothes, same philosophy of a place for everything, so I know where things are and I force myself to put things away once washed/ironed in the right places.
Our house is literally full of cupboards, drawers, shelves, racks, etc so there really is a place for everything. We're lucky in that it's not a particular large house, but there's 3 storage cupboards, two lofts, two garden sheds, and a garage, so between DH and myself, we've plenty of room to put some decent storage solutions in place, lots of those portable plastic/vinyl drawer units, boxes, etc., which we have fully labelled.
My problem is changing seasons when I change from a coat with several pockets to a jacket with just a couple, as that requires a change in mindset and habit as to where to put things.
Another trick, that ironically, our son "taught" me, was to "count" the items you take out, i.e. car key(1), house key (2), purse (3), phone (4), tissues (5) etc etc. I don't know exactly what they are, but he has a "rule of 5", i.e. he checks he's carrying 5 items before he leaves his flat, before he gets off the bus/train, before he leaves a cafe/restaurant, etc.
We're a family of it, as when we're out as a threesome, we're all touching our pockets etc to "count" we've still got the right amount of items with us. When in airports etc., DH is constantly fiddling with the tickets, passports, E11 cards, wallet, keys, etc as he's constantly mentally checking he has everything.