Obtain the page size of the book you will be illustrating for. This will help you create illustrations that correctly fill the size of the page or portion of the page the client wants. Identify if the book will be black and white or color printed. Creating color illustrations are often more costly than black and white illustrations.
Tape drawing paper to the drawing table. Use a ruler to draw the border for that particular illustration. Center the border in the page. Rough sketch the primary figures or elements of the drawing in pencil. Check your research material or the story in the book for accuracy in your drawing. Illustrate the figures in pen.
Scan the pen and ink illustration at 300 dpi. Save a new version at half the dpi. Open the new version in your art program. Set your new version layer to multiply and create a color layer and color your artwork. Delete the new version. Set your color layer to 300 dpi. Paste your original 300 dpi version of your artwork over your color layer and flatten the image. Save your image.
Tape down your drawing paper. Sketch your primary figures and check for accuracy.
Illustrate your drawing in pen and ink. Scan your drawing into the computer. Open the drawing in your art program and add other elements or delete errors in the artwork. Print out several copies of the illustration on watercolor paper.
Paint the illustration with watercolors. Because you have several copies you can test out several color variations to achieve the look you want. Scan the finished illustration for shipment to your client.