Improve your artwork by going back to the basics of design and visual story-telling devices.
A strong composition is vital to portfolio pieces that stand out.
Play with the size of elements in an image to enhance the mood of a story.
Find unusual viewpoints to create dynamic compositions.
Color and Value
Do you use color to express mood? Use color theory to help create sophisticated color palettes.
Use lights and darks to create atmosphere in an illustration.
Are your characters interacting with each other and their environment?
Study facial expressions to breathe life into your work.
Illustration tells a story, avoid still lifes or portraits.
Fundamentals of Composition - A great blog post to read.
Picture This: How Pictures Work by Molly Bang
The Encyclopedia of Writing and Illustrating Children's Books by Desdemona McCannon, Sue Thorton and Yadzia Williams