If you’re determined to find something, stop hopping from random inspiration to inspiration. You know, check under the mattress, then on the top shelf of your closet, then behind the pillows, etc. etc.
Mentally divide your room into cubes approximately a yard on the side, then search each cube in order THOROUGHLY. For example, say your room is 10’ by 12’ by 8’ tall. You have 3 by 4 by 3 ‘cubes’ to search. Start with one wall, and do the bottom row of cubes along that wall. Then do the next row of cubes that sit upon the first. Then the topmost row of cubes. Clearly some cubes will take little searching. Most likely the top row cubes will be either totally empty or only have a few picture frames to look behind. BUT LOOK ANYWAY.
Important: no assumptions! If the legs/seat of a desk chair are in the cube, don’t say “oh, the X can’t be there.” Nope. You must look and/or touch every bit of your cube. So look under the seat cushion, behind a back cushion, underneath the seat of the chair itself. (Hey! That’s right, I taped my passport there for safety.) Only when you’ve checked every ‘space’ within your cube do you move on to the next. Pick up every object, look under it, behind it, inside it. In fact, look AT it, a surprising number of times you won’t be able to find something because of false memories. You THOUGHT you were looking for a yellow hardcover book, when it turns out to be an orange paperback, that sort of thing.
The real advantage of this system is that if you don’t find the whatever, you can be sure it really isn’t there, and you can move on to other rooms instead of having that nagging fear that you simply failed to look at the back of the bottom shelf of that bookcase…
BTW, that’s where I’d look first – the hiding in plain sight method, you know? I often set books I didn’t want found BEHIND the rows of books. Also pick up and open every book that has a dust cover. Putting an innocuous dust cover around what you want not seen is an excellent disguise.