I'm very impulse driven seeing as I paint only as a hobby. I get to decide what I'm feeling for next! I would say that I try to keep it 80% comfort zone, 20% trying new things. That can be aspects of design, rendering, materials, lighting, composition, etc. The rest is almost following a recipe!
Also, if you keep things short and sweet, i.e. painting small/quick props or scenes, you can really follow the vibe of "today I'll draw some guns, tomorrow a character, and next week study hand gesture". You're always free to choose, until it becomes a job!