My favorite drill for adding distance is with the driver is to stand with the majority of my body weight on my trail leg using only the toes of my lead leg for balance, and without sacrificing the relationship of my hands/forearms/shoulders, initiating the most outside (relative to my ball-target line) takeaway I can create, and really being aware of the upper body rotation that continues after the hips have rotated to their maximum.
I encourage most of my physically fit and reasonably flexible students that do not present any injury to rehearse this drill with the knowledge that a wide, low, and outside of the target line takeaway is the most frequent opportunity for them to create width in their backswing and equally important; loading into their trail leg. The longer they can have their body weight and pressure inside the heel of their trail leg, the more likely they are to initiate the downswing with a rotational movement of their lead leg, as it is immeasurably more likely to rotate and not move laterally when they are starting down without having shifted the pressure from the trail foot to the lead foot.
I am not an advocate of drills for students without being intimate with their body movement patterns; I always screen students to see if they have a dominant leg, would they jump higher from both feet, or only one, do they have the physical ability to do what I am asking them to do. Most importantly I offer a few “homework assignments”, or “backyard activities” that are designed to help them become aware of their physical weaknesses, relatively speaking.
The last thing I will say about the drill mentioned above is that I want to make absolute certain each student understands that it is more likely for them to create a positive angle of attack when they are on their trail leg at the beginning of the downswing.