Here is how I create a painting:
1. plan the picture, small sketches to create the composition
2. nice sketch on arches hot press watercolor paper and sometimes I pick the colors I'm going to focus on
3. get the paper wet in the sink and flatten it out on a board. Get paper tape wet and seal the edges of the paper (this creates a flat painting in the end)
4. paint the background first. Here I painted the whole area with just water, and then added a color I had mixed a lot of:

I did the top background, then added another layer to the bottom for the floor area:

You can see on the sides where I test the colors I mixed before I paint them:



After it's painted I ink the outlines with a nib pen and acrylic ink:

finished:

scanned & cropped: