[quote name='Koggit']I had an interview with Big Fish Games but didn't get the job

[/QUOTE]
Me too. High five!
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Concerning making your own games, you usually start out with a high concept document. Its sort of like your initial pitch to the publisher.
Sample:
http://www.csc.kth.se/utbildning/kth/kurser/DH2640/grip08/HighConceptTemplate-Inl4.pdf
After that, when you get together with a few other people defining more specific elements of how the entire game is going to play out and everything associated with it, you create the game treatment document.
Link
As far as planning goes you'll also do story boards, come up with art assets, and anything else you think will help give a potential publisher/team members a better idea of how your game is going to go.
I am currently working on a game of my own, albeit very slowly. I'm basically learning the programming language as I go, and get easily side tracked with the more "fun" elements such as the audio production and artwork. I mainly use it as a source to pull portfolio pieces from.
Just a little look at the concept and implementation:
No expert by any means, but its fun and I will hopefully get to give it the attention it deserves at a later point in my life after I have established myself somewhere.
Made a couple of "trailers" for when I was presenting it just to try to set the mood.
This one isn't much to look at, but I was very happy with how that particular track turned out.
http://www.youtube.com/watch?v=_JkKdnFqK-I
I know SneakyPenguin is tn;td when it comes to making games, dude wrote his own game engine (I think). Theres also ReRo, though I'm not sure if he makes games so much as he makes interactive art installations.