Height and a nice, strong arm.
Perfect example = Mr. Ryan Leaf, QB for the good 'ol Cougars.
Having a good arm and the ability to see over the line is nice, but as said above, being able to read defenses is key. As long as the QB can get the ball where it's needed and keep the ball out of opposing players hands, he should do fine.
Failing to prepare is preparing to fail. - John Wooden