The director’s main focus during production should be on creative issues. Enter the first assistant director to take care of all the rest, or explain why they can’t actually have all the stuff that the director wants. In Pre-Production, the AD handles the script breakdown and scheduling for the production, working closely with the Unit Production Manager. Of course, that’s only when the project can afford to pay for both a 1st AD and a UPM, but either way, the 1st AD needs to have a firm grasp on the props, costumes and effects as well as when these things are needed on the set. Any technical questions about the production should go through the 1st AD. If it has nothing to do with character, story or visual style, then the 1st AD will handle it.
In Pre-Production, the Assistant Director needs to prepare to take over the project from the Production Manager. In fact, a lot of AD’s transition into production management, so it’s not bad to have someone who wants to learn. Ultimately, you want someone who doesn’t take too much crap from others but can also listen to any grievances. Yeah, it’s a fine line in the personality department, but you will make them a member of your wedding party if they get the job done.
Part of the Assistant Director’s job is to be a bit of a buzz kill for the creative vision team. If the creative types are looking for the coolest way to do something, the AD finds the safest and most efficient way. The director is in charge of managing the crew, but the assistant director is in charge of managing the crew’s health and well-being. But be honest with yourself: as much as this project means to you, would you want anyone else to sacrifice limb or even life to realize your dream? And if your answer is yes, you should consider casting yourself as the sociopath in your terrifying psychological thriller.