All I can say is: practice. Seriously, take it serious, and practice everyday, for hours. A lot of people talk about talent, but if you really delve into it, sports are all about discipline, practice and hard work. Talent is what gets you in (sometimes), and what edges you over when you've put i enough hours of work.
For positions such as QB, another thing you HAVE to practice in your head is conditioning. Keep thinking about gameplay situations, and training your brain in how to react. You'll see that a lot of times, the same things come up, and being prepared mentally to react properly, avoiding being blindsided by a defensive blooper and getting sacked instead of throwing out the ball or sliding/kneeling, is all the "talent" you need to push you through in the beginning.