So you want to design a game?

The main point of design is to be able to articulate fully what you would like in a game, at the same time understating the limitations of the project, such as length of time, amount of money, what styles your artists can pull off, what languages your programmers know, etc.

The most important thing is to create a Game Design Document. In the Document, you will outline what the game is, what kind of game is it, what kind of narrative will you have, how will it be built, and a rough time line of production.

Depending on Team Size, you may be responsible for creating the narrative and dialogue for the game.

Also, you may need to script actions for instances such as cut scenes or FMV sequences. Scripting is usually done in an interpreted language such as Perl, Python, Lua, or Ruby. Depending on the engine chosen for the project, one or more such languages may be used.

Emancipated Games' Design Forum is a space where you can ask questions and talk about Game design topics!

Game Design Document Resources:

Gamasutra: Creating a Great Design Document
GameDev.net Resources for Game Design Documents
Lost Garden: Using a Blog as a Game Design Document

Game Narrative Resources:
Man Bytes Blog: Game Narrative, Collaboration, and Storytelling

Scripting Languages:
Gamemonkey
Javascript
Lua
Perl
Python
Ruby
Tcl
VBScript