In Illustration, I generally work from reference. In other words, to get proportions correct, I will work from photos that I take, or photos from images that I get from the web.
I start with a composite image in Photoshop of how I think the image should look. Than I “flush” the sketch out thorough drawing and color.
Mainly, for book illustrations, I work in watercolor and colored pencil.
I also like collage, which I apply to the image in Photoshop along with text and color correction.
Above is the first pass at the cover. Village too small. Colors too close in saturation. Image is too busy. Red lettering too bright. To much too!
Above: Final Version.