While arm strength, how far you can throw the football, will always be an important measurement for a quarterback, it is not the most important.
As you watch the best quarterbacks, Payton Manning and Drew Brees, etc.
you will find that their footwork is their best asset.
Great quarterbacks will drop back, slide and step up into the pocket smoothly and effortlessly.
They seem to just move out of the way of the pass rush just in time.
Now, contrary to popular belief, they are not just born with some innate ability to get out of the way, but they have really spent hours and hours working on their footwork.
By doing this, their footwork has become second nature.
The hours of time spent running drills have taught the body to move in a fluid motion without moving their head to keep their eyes on the rest of the field.
This is why they can find the open receiver and make the crucial 3rd and long completion.
Some of the drills they use are: The Long Drop Drill - This drill forces the quarterback to practice his drop back for an extended period of time so that the body gets an extended feel for dropping back.
The Box Drill - These works all of the important footwork movements that help the quarterback get back to his throwing point.
Then he will slide back to another cone to practice stepping out of the way of the on coming defensive pass rusher.
He then steps up or climbs the ladder forward.
Again, practicing a short simple motion to buy himself that extra split second to allow himself time to complete the pass.