It should be noted that like anything, you can only absorb so much from reading. You do have to learn from your mistakes and get a feel for being a good GM. I've been doing this for a very long time and I'm [i]still[/i] learning how to do things better. 

To answer the second question, the most successful GMs have perseverance. Anyone can have a one hit wonder, but it's the ability to pull yourself together after a disastrous flop that lets you go on to make more RPs, hopefully even better than the last.