Disclaimer: I didn’t use traditional techniques or the proper tools for this! I actually use a Wacom Pen (again) and any sharp or blunt object I can get my hands on to emboss the leather. If you have the proper tools you can make it much more detailed or traditional but I actually like how this gives it a hand drawn look. It’s somewhat charming.
You could start out with the Tandy Leather Basic Set if you prefer to get the proper tools.