A place for everything
Until you develop your own working habits, I suggest these.
At the very outset, make a folder. If you havent decided what to call your design, give it a temporary working name. December will do, but Masterpiece or Abcd are just as good.
In your December folder, make these four folders.
If you use typefaces for reference, keep them in there. If you work from scans, save them in your Background folder, in a separate folder called Scans December.
The source document for your design goes into your Source folder. You may have one for December-Plain, and another for December-Italic. But your Source folder may only contain one of each style. This is important.
Sometimes its sensible to make a copy of your source document. But make sure you dont work on it by mistake. (Comparing two documents, searching for the most recent versions of each character, is a waste of your time.) Rename your copy, starting with the date: "94/12/23 December-Italic". Then put it into your Progress folder.
Like any sane computer user, you no doubt make regular backups. In addition, you should make an outline font (printer font, if you prefer) at least once every working day. It takes less than a minute. If you ever need to dig up what in heavens name you worked on last week, you know where it is.
Add the date and time to the name. Lets say you generated an italic font at 27 minutes past ten on 23 April 1994. Then DecemIta becomes 94/04/23 10-27 DecemIta. You put in your Progress folder. It is your record, step-by-step, of what you have done.
In the Tools folder you keep useful documents, such as text samples. You use them to scrutinize characters in large size, and judge texture in a column of text. Some will help when you space and kern.