Of course all of these tips won't quite directly apply to Byond programmers but they may be useful nonetheless..

1. Write games.
2. Cover the basics.
3. Achieve intermediate level in C++.
4. Never stop learning.
5. Communicate.
6. Tools of the trade.
7. Work with a team on a large project.
8. Play and study games.
9. Pick an area of expertise.
10. Get a well-rounded education.

Greater detail at the link:
http://www.gamecareerguide.com/features/724/features/724/ top_ten_tips_.php