When I lose my keys, I try to remember what pants I was wearing the last time I went out, then search for them in the laundry basket or in the place in my closet where I leave pants I have only worn once or twice. Usually they will be in one of those pockets of that pair of pants. I usually go out daily, so I don't have to think back that far.
I leave my phone in one spot in the house, as if it were a landline. I religiously use the phone right by that spot as if it were a landline and put the phone back there when I am done. If I take the phone with me, I have one spot in my purse where I place it, and I make sure I return it there when I am done until I return home, at which I place it back in its "home" spot. I rarely take it out of the house, only if I have to go out and am expecting a call. Otherwise I leave it at home.
For years, when I was not so far along in therapy, I did not do these things and when I could not find my phone or my keys, I either went nuts, or went and asked a neighbor to call me, so I could hear where my phone was in the house and find it. Once recently, I had my phone in my pocket (forgetting my rules) and it fell between the cushions on my couch. My neighbor called me and called me, until I found it by its ring. Now I am more strict than ever about my phone, because I don't always get a call every day and the battery could go dead if it were to disappear again, so I check often that I have placed it where it belongs. I also check to see how charged it is, so I can charge it if it is low. I check that every time I use it. These are hard won fast applied rules I have made in my life, after many mistakes made beforehand. I still goof up now and then, but thankfully (usually) I catch myself before it is too late.