STEP 1: FILE SETUP + SKETCH
FILE SETUP: In Photoshop, click File-New. In the window that pops up, ensure your document is set to at least 300dpi and set to CMYK color mode for print or RGB for digital display. (You can always convert between the two later.) If you are doing an 8" square book for example, set the width to 16.5" by 8.5." This allows for the whole spread to be visible in one document and also adds .25" bleed on all sides. (You can always trim off but you can't add more after printing!) I like to draw red guides along the paper edges where the bleed starts, and a line through the middle to represent the gutter, where the pages are glued into the spine. Make sure no important illustration elements or text falls into the gutter!
SKETCH: Before color, I prefer to flesh out a sketch to act at the framework. It keeps my workflow more organized moving forward. Create a new layer and label this one "sketch." In any illustration, the sketch is always most important-it lays the entire foundation for the rest of the illustration! Take your time drawing and brainstorming the composition on this layer, and work from loose, general shapes, and eventually hone your linework down to a clear sketch image. Here I used a 3 pixel black calligraphy brush. When you have something that you feel clearly represents what you want your illustration to look like, you're ready to dive into color! Note that not everything has to be fleshed out in sketch. Things like clouds, or other small details can be represented directly with color-no need to sketch every little thing! At this point we want to ensure the author/client can see your sketch and understand what the image will look like when colored. It's a lot easier to get their color approval when they can clearly see what your sketch plan is for the illustration! It's your job to visually communicate, so try to be as clear as possible in service of your author.