The initial Game Design process is the most significant step. Without a solid game design, all the shiny bells and whistles added on top of that piece of crap still stink. Here are some of the sessions I went to that helped me develop my craft even further.
The separation and distinction between theme and mechanics is crucial in developing the right game. Soren really drove home the concept: mechanics of the game are what gives the game meaning and life. It’s interesting though that our first reaction to categorize a game is by looking at it’s theme and appearance and not the underlying game mechanics. As a player, you will often be disappointed in your assumption of a game based solely on theme. If you take a step back and analyze the game’s mechanics you will see really what the game is about.
I really enjoyed the slides in which he would state that a certain game is not about something, but rather something else (Left 4 Dead is not about Zombies, it is about Teamwork). Soren was able to show that if you strip out the theme of a game, its mechanics still gives it meaning, but not the other way around. You can download his slides here. Here is a good summary of the session at Destructoid.