To me, this is a critical thing. How are you supposed to find your things if you don't have a designated spot to put your things? This is why I suggest putting your items in specific places that will be where the item stays whenever it is not in use. Try to put these items in places that you will be able to remember easily and maybe label that area if you have a small item. 

(Sorry, not the greatest picture) This is a new Idea that I recently came up with. I think that this is important because this is basically your "Find my iPhone" app, instead it helps you to find your things. Make a list of things that you borrowed from people and where they are and make sure that you stick to it. If the place changes, you should also change the list. Another thing that you could do is to add the due date on when you have to return this item.

You should do this so that you know if you are bringing important items out of the room and you frisk yourself and it is not there, you'll know that it is in the room. "In theory" Maybe do the "3 Things" checkup by checking for the three most important things (Or 4/5/6/7/8, You get the picture) I have tried this before and it has helped me to stop myself from leaving the room without important things.