Of course their primary concern is germs, but surgeons also report that the cleansing helps them reach the proper state of mind for peak performance. When a weaver leaves a cloth half-finished, she carefully leaves a thread dangling at the point where she left off. When the weaver returns to her work, the dangling thread allows her to resume where she left off. Some authors end their day's work mid-sentence so that they have a natural starting point the next day. When you near the end of your work day, look for a thread of your own to leave dangling.
Ideal candidates are code which is fairly straight-forward , or particularly enjoyable.
This should be a note, preferrably in the form of temporary comments in the code itself, which describes what you are currently doing, and what you think should be done next. These notes don't have to be highly formalized or long, they only need to persist your mental stack until you return the next day. Your mental state, and your mind's ability to create, is closely linked to your environment. Therefore, if you want to reach optimal performance, you should control your environment. Hypothesize about how your environment could be more optimal.