Although highly important, this idea is pretty self explanatory.
The main idea is have a place for everything and keep everything in its place. And a related idea is to keep things close to where they are likely to be used the most. Putting these two concepts together, I try to store like things together while keeping important things easy to reach.
Sometimes important items are used in many places, in which case I will often have more than one of the item, if practical. For example, I keep a pair of reading glasses in several places: my car, my bedside table, my study desk, my office desk, my piano, and on my person.
Labeling is also important, although there are many ways to do it. For example, sometimes I use simple sticky labels. But I sometimes use clear containers, which can avoid the need for labels. And for very large collections of “stuff,” I typically put everything in bankers boxes and then number the outside of the boxes, while keeping a reference sheet that says what is in each numbered box.
(For example, I recently stored about 70 boxes of personal items in a storage unit. I numbered the boxes on the outside, and then I put a post-it note inside each box, showing the box’s number. Next, I took a picture of the inside of the box, which showed both the number of the box and its contents. Finally, I combined those pictures into a single .pdf, which now serves as both a numerical and visual index. This is discussed in more detail in my post on Storing Boxes.)
One Idea 