When you start chiseling the leather, make sure that you follow the cut lines exactly or you will end up with a sloppy looking project. Hold the chisel perpendicular to the leather to mound the leather on each side of the cut line.
Use a rawhide mallet to punch the leather out on each side of the cut line. It is very important that the leather be damp at all times during this process. You can keep a glass of water with a paint brush in it near you to use if you don’t want to keep getting up to dampen the leather.