Early on I realized that trying to paint normally as one would with a brush wouldn't work well on vinyl. It ended up looking blotchy or too thick. In the back of my head, my high school art teacher's favorite project helped me figure it out. Dots.
I've described my work kind of like a reverse newspaper photo, with the density of the dots of paint creating the illusion. What was this project Mrs. Kahn loved so much that gave me the idea? Using only dots to create drawings with a very fine point rapidograph pen. I was in her elective class 3 years and each year we'd do these things and have a book printed of the whole classes' work. They were insane.
The idea stuck in my head from such a repetitive action so much so that after high school I actually was planning on trying one with colored ink. Yeesh. But, the theory is really useful. With enough care, volume can be created with smooth surfaces, and edges can be defined without solid lines. Indeed, the best lesson for me from the whole thing was that using lines to create shapes truly flattens objects, breaking the illusion of real substance.
This, along with my lessons from sculpture, are why I start in the middle of shapes and shade outward, bringing the volume out of the dark into the light.
It's also why I have to paint to music with a beat to it to drive my wrist's repeated dabbing.