Here is a good beginner tutorial on working leather. In addition to making the basic project, the author (Weaver Leathercraft) iterates on the design, refining the pattern and adding features.
This is a good intro on making a simple leather project, and covers setting rivets, setting snaps, grooving for a sewing line, hand stitching, and especially showing how to evolve a project and make enhancements.
It packs a lot of useful advice into a 28 minute video.