Now this may seem like a pretty freeform process but there are a couple cardinal rules.
One: Under no circumstances do you clean your brush. You want to get those random, accidental color mixtures that occur in nature; you know that purplish shade of orange or crimson teal. Like a mixture of mermaid spit and jackalope venom.
Two: Don’t clean up after yourself. The paint will dry pretty quickly and you want to be ready to move when it’s just right so drop that empty paint cup and keep moving forward.