I have discussed memory a bit, that we do not remember remote events anywhere near as well has we think we do and some of the reasons for that, but i don't think I have ever shared my little tricks on the matter.
When you can't find something and have looked in all the good places, do not then proceed to the medium-good possibilities. It won't be there, and that method will simply reinforce the incorrect memory tracks that didn't work the first time. You will find yourself looking at those "really good places" six or seven times while you are checking the medium good ones. Look in the utterly stupid places instead. Look under the car. Look in the refrigerator. Pull out the paper slips for your financial records this year. Those will break the seal and allow your brain to remember the unusual answer. "Oh yeah, I put it in the pocket of that light jacket I never wear but threw on yesterday to go to the store when it was raining." If a half a dozen stupid places don't work, you likely have to stop and do something different for a half-hour. But I usually find that the stupid places do reveal the true answer.
This is explained by what is called state-dependent learning, related to the idea that if you learned to play darts drunk and became good, you should always be drunk when playing a game you really need to win; or that if you stayed up late and were angry studying for a final exam, you should make sure you are angry and tired when you go into the exam. It works in the negative as well, that your imagined "best state" for remembering probably isn't and you need to switch lanes. Obviously, if you have a routine for exams that has worked in the past you keep rolling with that, because that itself has a state-dependent quality. Yet in the absence of that, revert to the learning environment.
Secondly, once you have found your lost item, make sure you start storing it in the first place you looked, because that is where your brain thinks it should have been.