When doing a veneer case or any type of smile makeover, you always need to begin with the end in mind.
Veneer preparations are based on specific reduction requirements, BUT those requirements are based off of the end goal for the smile. So veneer preparation is influenced by the final outcome that you and your patient have agreed upon.
Once you understand the end goal, you then work backwards.
If you understand what your final smile is going to look like, then veneer preparation simply becomes making room for your restorative material.
This is especially important as you consider no prep, prepless, or minimal prep cases. The concepts of smile design, understanding function, patient goals, restorative space, esthetics, and reverse engineering are all key in understanding veneer preparation.