Let's say the aim of a drill you're running is to improve skills (as opposed to say, getting warmed up for a game).
Ideally the players get lots of opportunities to practise the skill you want them to improve. Improvement requires practise of the skill. This is not rocket science.
To do this, you should minimise standing around and queueing.
One of my bugbears is seeing drills run for beginners that require only one disc. Not only is 18 players using 1 disc an inane idea, if there is a drop or poor throw, 17 players get to stand around even longer watching one player jog over, pick up a disc, then jog back to the drill. The drill is stopped by an error. And errors happen with beginners!
Therefore I am proposing death to dump-swing-score. There are so many better drills out there.
In general, pick a drill that requires multiple discs. The drill usually won't be held up by an error. And the number of disc touches per player per hour (TPHs) will be much higher.