I just wanted to add some interesting links. These are focused on game design paradigms (e.g. patterns, game mechanics) and heuristics (e.g. rules, guidelines) which are by far the most often developed in an effort to better understand game design, whether they are the most often used tool, I am not to sure about that...
Game Design Paradigms:
SCVNGR’s Playdeck
(SCVNGER's Playdeck w/ Gravity 7s Comments)
5 Creepy Ways Video Games Are Trying to Get You Addicted
Strategic Synergy's: Game Mechanics
Game Theory Dictionary
20 Underused Game Mechanics
Top 10 Research Findings 2008, 2007, 2006
Shinji Mikami On Mechanics
Game Design Heuristics (Tips, Rules, Guidelines, Commandments, Pitfalls):
The 7 Commandments All Video Games Should Obey
The 400 Project (Noah Falstein)
Rules for Game-Based Systems
Sid’s Rules (Sid Meier)
Game Tuning And Design Tips Iphone Apps (Taisuke Odaijima)
Seven Creative Tips for Amateur Video Game Makers
Game Design Tips (Jesse Schell)
10 Game Design Process Pitfalls (Ian Fisch)
Pitfalls of the Working Game Designer
The 10 most common game design mistakes
[Level Design] Capture the Flag Level Tips
[Board Game Design] Andrew Looney's Eleven Principles of Game Design
[Board Game Design] Design Considerations (Greg Aleknevicus)
