“The quality of practice is directly related to the amount of time you spend thinking about the practice itself, preparation and organization are key.”
There is an old coaching axiom that you should spend twice as much time preparing training as the training itself takes. So for a two hour training session you should spend four hours preparing. Sadly the effect of this and most coaching axioms (and popularly shared quotes by famous coaches) is mostly to make coaches feel inadequate, but the principle is sound.
To spend twice as much time preparing as you do training is impractical. For most coaches, there are simply not enough hours in the day. But planning each training session is essential. In addition to that planning time, it is equally important to spend some time reviewing and reflecting on what the goals for the session are, what will be the key feedback points, where the drills will mostly likely break down, and how exactly to manage those and other situations that will likely come up in practice.
By going through this process, the coach will prepare the best possible practice and prepare themselves for the task of making the team better.