I prefer using star or split lock washers. They can be had in finishes that matches many colors (mainly chrome, nickel, zinc plated, gold and a variety of blacks). Some types (mainly the stars) will have limited availability in some finishes.
For those applications that dont have enough threads to add such washers, I use a dab of easily available clear nail polish, a little goes a long way so don't apply too much else twill be even more difficult to remove (idea here is to prevent it from working lose from the vibrations the guitar is experiencing, NOT make it unremovable without damage to the guitar itself).
Great advice here like use a tooth pick or tape or something non permanent to keep screws in place. I would add that not to over tighten the screws or the screw could make the hole loose.
I'll try some clear nail polish, since that makes sense in my mind. Strong enough to keep things in place, but brittle enough to let it come loose if needed!
I really appreciate you all, and this forum,
sincerely,