I keep a sketchbook of ongoing project ideas with me most days of the week. Whenever I have a good idea I sketch it or write it down. Sometimes my planning is more precise with finding reference photos and sketching layout/composition ideas. At other times my projects are more loosely based and I let the process of the piece and conditions within it guide my intuition.
I usually paint and draw with music on and I’ve been known to be gone for hours without realizing they’ve passed. I love how artwork is a process. I do have a general idea of how a piece might turn out, but along the way there are challenges and pitfalls that change the piece in interesting ways which I find creates a character of its own.