Author: Mike Sellers, a game designer for over 15…

Inspiration can come from daily life, from taking a walk or a drive, from playing another game, from seeing a problem that can be modeled in a game, or from the ever-present “wouldn’t it be cool if…” Another useful way to get ideas is to set constraints; many people don’t do as well as you might think with a completely empty canvas. So choose limiting conditions, even arbitrary ones (you can always change it later). So: this is a game about flying. Everything in this game is a shade of blue. The game is about loss and rebirth. Just typing those (at random) you may have three new ideas for games you could spin from them — and other people would come up with ones that are completely different from yours.

All that said, and not to sound flippant, but the problem isn’t coming up with ideas — it’s sorting the bad ones from the good ones, and then focusing on one good one for long enough to turn it into something. For most designers, ideas come in an unending stream. It’s like a fascinating and frustrating firehose of ideas that you can’t really turn off. All you can do is quickly scrawl down your idea (cloud creatures living in twilight, rotating with the earth, dying with the night but being reborn with the sunrise — etc) and get back to the idea you’re supposed to be working on.

source: http://www.quora.com