I usually make an enlargement of my pencil drawing to transfer onto the watercolor paper via light box. I then like to take that copy and draw on top of it a lighting study which will be my guide when I paint the shading.
After all the art is transferred I paint all the line art.
As you can see, I completed all of the line art across all of the pieces (reusing as many of the colors as possible) before moving on to the next stage.
Next is the underpainting. I use acrylic wash to slowly build up all the shading and values.
Again, I do this for all the pieces.
Lastly I apply Luma concentrated watercolor. It's completely transparent so it retains all of the acrylic shading perfectly.
Of course this whole process took me weeks because there are twelve pieces (plus a bonus) but I finished them all at the same time!