As I work through a project I assume (1) I'll do this again someday and want to remember how I did it and (2) I won't remember how I did it. Therefor I try to document my work as I go through the day.
I take an old brief case to the shop. It contains an old digital camera, correction pens, ink pens, 1/4” ruled graph drawing pads, some files of currrent projects, the things I use to document work on projects.
The camera is dedicated to the studio. It's taken a lot of abuse and has some annoying faults related to the abuse but If I had a good one there it would soon suffer the same fate. The images are usually good enough to record a series of steps more exactly than my writing would and it is faster to accomplish. I'd guess I usually snap a half dozen photos a day.
I’ve never found it a problem to pitch extra notes but it is a problem to try to remember what stock I used on a project two years ago when the customer wants another one just like it made. I try to be seriously methodical in writing notes, clearly noting the stock, measurements, tools, dies and mandrels used in the forming process and the finishing. I record the approximate time required in each step. This is essential for pricing.
When I am satisfied with a design and plan to make it again, the dedicated project box is one of the easiest ways to document that work. For instance, I recently made about thirty Conestoga wagon wing nuts for a project. I pulled out the pressboard cover file made a few years ago and went to the cargo trailer to get the plastic box which contains some blanks, the step set and most of the required tools. The finished hardware pieces must look self similar and this method takes all the guess work out of process.
When any work is completed I reflect on the experience and identify how it might be made to look better, or how I could create it more efficiently and record those thoughts too. I then print up a report and hang up any useful test pieces in the studio. Those are my “sketches in iron” or the library of visible solutions.