All ideas start with brainstorming. Since this commission was open ended in theme, I had to do some 'soul searching' for what I was interested in working on, and give myself limitations. Then it's a case of how to approach the composition of the piece.
Eventually, a layout pops out of the rest. Now it was a case of refining the focal points (rule of thirds definitely helpful here), sketching out the final draft, and doing an approximate colour test, and finally moving on to line-arting and colouring the final piece.