From Marc Swackhamer:
1. Start with something concrete.
2. Overlay diagrammatic information.
3. Focus on the things we cannot see: cycles, time, movement, change over time, spatial characteristics/descriptors (fast, slow, thick, thin)
4. Pull out information you do not need (important to use layers). Use just enough contextual information so that the viewer can orient him/herself.
5. Minimize text / Minimize arrows.
6. White space is your friend.
7. Use color sparingly.
8. Don’t be afraid to invent notational systems or new ways to depict information.
9. Don’t confuse clarity and simplicity for simplistic — a good diagram can be rich, complex, and deep.
10. Do it again… and again…