From a simple perspective one can approach acting training from two angles: psychological and physical. Having been trained in both early on in my career as an actor and director I have a very specific preference:
The physical based approach.
There are many reasons for this, primarily, one can never escape one's body when in performance (from VO to theater to on-camera work). Therefore, it is logical and appropriate to start learning from our physical self to improve all of our performances.
Beyond logic, I've found in my 20+ years of teaching that working with the actor's body builds a lifetime of better habits/skills and furthers any artist's main need: a better understanding of one's self.
Building characters from the "outside in" instead of the "inside out" creates grounded, actionable, directable choices and actors.