Quick bit of advice for the serious GM, counting on a good role-player to make a decent game is not a decent strategy towards successful gaming sessions. Of course, you as a GM, have to know when throw the script out the window and just let the players do what they want. "Character building" should never take the place a story to be told. If you're sitting down to a table with only an inkling of a premise and waiting for the folks to provide you with a plot, you're most likely not in the mood for a game, as well as about to be very disappointed.
Even the most narcissistic role-player gets over the joy of being catered to in about 20-40 minutes, depending on the size of the ego. Dealing with, say, four players's whimsical cravings for about 20-40 minutes _each_ only increases the length of the overall task, not the enjoyment of the session for anybody. Doubt that last bit, watch a bunch of kids play Cowboys and Indians (TM Hasbiro, 2015), or Tea Party (TM White Wolf 2015). Use a stopwatch and time how long before swear words, fisticuffs, or playing with matches replace the role-playing. For those over the age of 13, twenty minutes of daydream fulfillment is about all the person can indulge in before getting sleepy. Hopefully you've got some reason for the players to use swear words, engage in fisticuffs, and light fires. If not I hope you brought along a kewl board game.
Where does the GM get his story from? It can be as simple as a random table with a whole bunch of mentions from the players, but it can't be from totally "winging it." If you ever watch people enjoying a RPG session, besides the Monty Python quotes, people really enjoy picturing something in their heads that they hadn't thought of before. That last bit includes the GMs, but that should be from surprise Character moves or randomizer results, not the story being told to him.