I learn a while ago, the hard way I might add to keep notes while I work in the shop. First it was a spiral notebook like the one you get for school. I have three of them now, full of old shop notes, mostly notes and cut list from old jobs I have worked on. I also have a three ring binder that I paste pictures of furniture or other things that catch my eye. I keep sketches of furniture or what ever else that I think will be useful to me when I am working on designing a piece in this folder also.
Last year I found this little notebook that is filled with 1/8″ graph paper, its small with a hard cover just the right size to keep in my toolbox. I really like to have this available while I work, mostly because that is when I find I am at my most creative. Its usually when I’m visualizing what I am building that I start coming up other ideas, some of them related to what I am building and some of them not. Having a notebook close by lets me jot those ideas down for a later use. This book is also where I write all my job notes and figure out the layout for cutting plywood so I can get the most yield from a each sheet ply, something I have found that saves me time and material. Having these notes let me reference a piece quickly in case I have to cut another piece for when I screw up. Plus if I get other cabinets the same size I all ready have the cut list. I also keep track of operational times which help me estimate future jobs.
I urge everyone to start keeping a notebook in your tool box and after a while you will find it will becomes a part of your tool kit just like your saw and plane is.