From a practical standpoint, revisiting the elements and principles of design can also offer inspiration when faced with an empty piece of paper.
Refresh your understanding of point, line, plane, shape, form. In fact, you might even enjoy a story created around these characters. Flatland by Edwin Abbott is available as a free download because it is in the public domain.
Taking the element discussion further, consider color, value, texture, and of course, image and type.
The principles of design describe the effects and relationships that are created by the elements interacting with each other. You should be able to evaluate and discuss your designs using these terms.
If you need a more formal refresher, take a look at Ellen Lupton’s book and companion website, Graphic Design: The New Basics.
And read about the Gestalt Principles of Perception starting here. A very good writeup by Andy Rutledge.