Below I show you how I turn my images into Christmas watercolor illustrations. My usual process is to brainstorm, use artistic license, combine, add or remove items from my photo, make it abstract, avoid painting shadows and values etc.
The first illustration is based on a photo I took from a decoration shop showing a reindeer sitting next to a crystal ball. I changed this photo by replacing the red cardinal with a home, which made more sense to me showing a reindeer missing its home in Christmas.