A very useful book is 'Fiebing's Fantastic Finishes' by Tony & Kay Laier: exemplifies the steps for different types of leather dyes: alcohol, oil, or water based, resisted ('blocked') or not with Leather Sheen or Tan-Kote; also the use of Acrylics and Antique Finish.
If I use water based dyes I dilute it with water until I obtain the desired shading, step by step working light to dark. It's best to test the steps on a test piece of leather first.