A genius idea can happen anytime and everywhere, but an idea is not a game...
1: Always have something to take note or draw an idea.
2: Test the core gameplay mechanic with a prototype. The prototype is a good place to start. It validate to yourself if the project has a potential and if it's fun. If you test and it sucks, try another idea.
3: Ask a friend or comunity users if they like it. Post a prototype to the Scirra Arcade service and ask comment only related to gameplay.
4: Create a Game Desgin and level document.
5: Now you have something, don't waste your time on graphic and visual at this time. Just build the levels, menus and code.
6: Balance your game and keep learning on everything related to videogame.
7: Make your game pretier, try the first level, then post a DEMO. It's the second test to know if people like your game and it shows that you have worked on your game.
8: Found the best options to publish and promote your game.
9: Open a bottle champaign and spend all your money considering that your game has made you Rich $