Here's a rough step by step showing my process for my latest piece.
I knew from the begging I wanted to have a horse carrying a bunch of stuff and a figure. So I started sketching that first.
I then added a background to paint on, and quickly sketched where i wanted my other figure in relation to the first one to make a pleasing composition.
Then it's painting time ! As you can see I changed the horse quite a lot in the process, and the women too (especially the face at the end)
The last step is all about the tiny details that put everything together : small background elements to make the painting less "empty", birds (because it's not a good concept art if there's no birds) added more color in the foliage and finally color correction and Voilà !