Alla Prima: Everything I Know About Painting

It teaches you how to OBSERVE 3-D REALITY AND TRANSLATE IT ON A FLAT SURFACE AS DIRECTLY AS YOU CAN. The way of achieving it is to paint LIGHT ITSELF (what you see), not the very object with descriptive minutiae (what you know). Meticulous and painstaking painting tends to be naive in most hands.
Schmid asks you to clear up your mind and trust your instinct. THE HOW BECOMES OBVIOUS ONCE YOU UNDERSTAND THE WHAT AND THE WHY.
Some of his most insistent advices are: keep it SIMPLE; don't overwork; don't use ostentatious techniques; don't make random guessing brushstrokes; do a minimum of trial and error (correction wastes time); rather be BOLD than shy, but do it without hurrying and without any thoughtless bravado. Also, EXCESSIVE BLENDING IS LIKE MUMBLING WHEN YOU SPEAK.
He teaches you that, as you start, you sholud focus on one specific problem. Set a GOAL and do it in the time available. Limiting your time helps to SIMPLIFY your works. Simplify values by SQUINTING. If edges remain sharp when you squint, paint them sharp; if they go fuzzy, paint them fuzzy. Trust your squinting.