The best place to start with the QB is to understand this athlete needs to have great hands and love to block (aka hit people). We are looking for a smart, smash mouth player with receiver like hands who can lob a football in the general direction of a receiver. Note that I did not use the word "pass" as throwing is not a necessity; however, between two players who have all the other characteristics we will use the better passer.
The reason we don't care about the QB's ability to throw the football is because he will spend all of his time catching a snap on the run, pitching the ball (which is not the same as passing) and lead blocking on most plays. We identify this player early on and then teach him how to throw the football. He almost always is not the same player we would use as the QB in the spread formations. We tend to use our best blocking up-back in the spread as the QB in O'Brien.
It will take no less than 500 QB / center exchanges to get the pace and timing right. This is not a position you simply plug someone in and expect the offense to run smoothly. This is why we like to have no more than two centers and two QBs on any team getting all the reps. This is a player who is expected to know the blocking assignments for all other positions. The reason is he will be making the decision post snap as to where we will be running. This point needs to be reiterated. We change the designed hole to which the runner will be running after the snap depending upon the blocking. The QB can only make these reads by knowing who every player is designed to block against all defensive fronts.
Coaching Note: When selecting the QB, you start with 1. ability to catch a ball, 2. student of the game / quick learner 3. desire to hit and 4. ability to pass.
The mechanics for the QB will change depending upon the play called and the remainder of the positions in the offense can be filled with varying level of talent. For example, one year I had a slower running back because my three best runners were my three best blockers. We annihilated teams simply because it always looked like the parting of the red sea when our back hit the hole. He was often taken down after a 15 yard gain but he almost always got more than ten yards.
The next step is to understand the roles of the RB and FB.