step 1 sketch
step 2 reduce transparency of the sketch layer
step 3 use pen tool to draw color *one color blocks one layer*
step 4 finish the generally color
step 5 refinement it *one line one layer* and delete the he excess of color blocks
step 7-step 9 Ibid
step 10 substantially completed,then make texture for it.
step 11 To use brushes make texture on color block.
step 13 done
Hope you enjoy it