Whether your house looks like this or is as tidy as a show home, we all lose things. I'm often guilty of having something in my hand one second and losing it the next.
So, onto possibly the most useful tip of all - definitely one I often repeat to myself and my friends, and anyone I find searching. It's alarmingly simple - to find lost items, lift things up. Lift everything up, one a time. It doesn't take long and you'd be amazed how often then thing you're searching for has slipped under or behind something else.
So get lifting. (And if this fails you, you can always do what my grandmother swears by and ask St. Anthony for help... it's worth a shot.)