I was reminded the other day of "where to start" with an idea regarding game design and conceptualizing out your game. I was remembering a great bit of information on the topic that was instrumental to me at the time I was getting my feet off the ground...
Ian Schreiber, besides being a pretty nice guy in general, shared some pretty deep thoughts and analysis on game design in a very grand 'global' experiment a while ago in which I only partially participated in. I always regretted having to choose the path I did that took me away from it at the time, but revisiting the material has been invaluable over the years.
http://gamedesignconcepts.wordpress.com/
I really like this book co-authored by Ian Schreiber and Brenda Brathwaite (soon after Garner, now Romero):
http://www.amazon.com/Challenges-Game-Designers-Brenda-Brathwaite/dp/158450580X
It all takes a step back from the computer a bit (and that is a good thing sometimes!), but I haven't found a single thing that didn't translate in some fashion. And the techniques on troubleshooting and verifying mechanic, although laborious, I have found worth it.
There are certainly a lot out there. But these two sources have a common voice by Ian and I like his attitude (and Brathwaite has pretty epic contributions to the industry as well and deserves more than a foot note here, but this about Ian.) Someone who manages a production schedule might go insane, but you end with a quality product given the emphasis on testing and evaluation.
Here is your entry point that is as good as any of the best entry points I have stumbled across in my searches yet.
You are welcome.