I think every laptop I've ever worked on has had numbers next to every screw which indicates which screw size goes there. So I can just sort screws by size as I take them out, and if you remember at least one of each size, you know which one is which (usually the numbers indicate screw length). I also sort them based on what part they were taken out of -- screws for the base plastic go in one place, screws that hold the LCD in place go in another.
Beyond that, I just remember where I took screws out as I work on it. I think I've only ever left a screw out once or twice, though sometimes I put a screw in early and have to take it back out in order to place another part under it, like an EMI shield.
If a particular cover or part is secured with a couple of screws, it's easiest to place the screw with that part, like a hard drive or the memory slot cover. But for other parts like the main base plastic, you just have to collect them together as you work, so a small container works.
It is always a good idea to have plenty of space to work of course. That makes it less likely that you'll accidentally slap a pile of screws with a part and send them flying.
Just remembering what you took out is probably the worst way of doing it of course, but it generally worked for me. It can be confusing though, since there are often holes where it looks like a screw ought to go, but where you aren't yet supposed to put one.
If you get certified on a particular brand (such as Dell) then you end up usually getting a bunch of parts listings for all the models which also indicates exactly where all the screws are.
