1. Read books on game design regularly
  2. Write regular blogs on game design
  3. Chat with other game designers
  4. Design small games revolving around 1-3 simple concepts
  5. Play games to analyze them. Break them down into constituent parts
  6. Read blogs and articles about game design
  7. Do regular creativity exercises about the project on which you are working
  8. Brainstorm game concepts
  9. Read books about psychology, group behavior and human-factors engineering
  10. Read postmortems from game designers
  11. Find a mentor
  12. Go to conferences (even if on your own dime)
  13. Take art and creative writing classes
  14. Practice public speaking
  15. Define the skillset a Game Designer needs to have and rate yourself for each skill
  16. Ask your boss how you can become a better designer
  17. Learn some programming
  18. Learn more math and statistics
  19. Learn more physics
  20. Keep your workload to 40 hours a week or less. The first victim of overtime is your creativity
  21. Make your own list like this