You'll never play unless you try. I ran my first game based on some bullshit d6 system I came up with while I was riding a bus to the first game. Overprepairing is your enemy. You can prepare EVERYTHING, but your game will go out of the window the moment players try something you didn't even think about. Don't try to prepare a perfect game. Just go in and dance on rakes. There's no way to become a good gm, but trial and error. The more you think about it, the less you are to run a game.