I don't think there is a good answer. Maybe if you've got 3 or 4, you can store them where you can see them. As the number goes up, its even more difficult than storing your handguns. At least guns won't poke holes in anything you put them in.
We moved 2 1/2 years ago, so I didn't like the idea of keeping them separate from the sheaths. Mating them back together was a time consuming pain, one I didn't have time for. So I ended up putting them in knife rolls as a temporary expedient. Then when I finally retrieved them from my son's house, I decided to try to reunite them with the correct sheaves. It was a real pain.
Randall does make a knife sheath (in different sizes) that allows you to put the knife inside and on the back (or the front depending on how you're holding it) it has two elastic straps. Those are for putting the sheath in and holding it with its knife.
With Randalls, its sometimes kind of easy because the sheath often has a model and a length stamped on the back (like 4 6 for a model 4 6"). But it only works if you got the right sheath with the knife.
So as I progressed I discovered that my buying style didn't include me paying proper attention to what I was getting. I ended up with what looked to me like having 4 extra 7-4 sheaths. I do have an orphaned Trout and Bird, but its a very old grind, unlike todays and I'm certain it didn't come with a sheath. I does fit in a 7 4 sheath, but I'm certain I bought the sheaths from a knife purveyor with my 6 4 steak knifes.
So after all this discussion, and my experiences, I'd advise keeping the knife and its sheath together, not separate. What happens is you think your memory is good enough to keep 2 knives and 2 sheaths straight. But as the numbers grow and your remembering power fades, you wind up with a mess. Besides, its nice to be able to look at your knives and pick the one you want. Without digging and looking for hours to find "its" sheath.
The other rules that apply. If you've used the knife, wash it well, in hot water. Hot enough to evaporate the water as it dries. Its OK to use wax or gun oil, but sparingly. And depending on the handle material, you might be better off going slow. Wax in cracks or places like stag or leather washers is bad.