so after 13 responses of "less talk more action" how about some other input on how instructors actually keep the class from being boring?
I like to pick one thing to work on, then work on it in different ways.
One day I may pick a technique, say a wrist lock. We start very simple, other guy reaches, you get offline, parry, get the grip and apply wrist lock. Let them practice many reps. When most have it somewhat... use the wrist lock to a take down with it. After reps there, do wrist lock, take down, turn the guy over. Next do wrist lock, take down, pin. Keep the initial attack and technique the same, but go different places with it. This helps the student feel like the class is moving along. They think they are learning this cool combo. In reality, they are getting lots of reps on the same technique. As they start focusing on step 2 and then step 3, they start doing the first technique without thinking about it. You can also space out the details. (to get them to turn over, the trick is to set it up, get the grip correctly when you start the wrist lock, keep the tension and grip as you take them down, now the turn over is easy)
Another day, I may pick a principle, say getting offline from a straight attack. First, do reps with a punch to the chest, and you get offline. Then do reps, where you get offline, move behind, catch the shoulders and throw them back. Then get offline, catch the punch and arm bar. Then get offline, catch the wrist and do the wrist lock we did last week... Get offline, throw o'soto gari. Here they are getting lots of practice getting offline. Same as before, they are getting lots of reps of the principle with realizing it. You can spread out the details.
When doing either technique of the day, or principle of the day, focus most of your correction to that, not the rest of the combo. Keep focused on the principle or technique. The rest of the combo may look pretty funny at first... just keep it safe. It will give you ideas for the next technique of the day when you see they all have issues with this piece of the combo. At the end I like to let them know what we were working on. Have them go back and do the initial technique, and realize how much better they are at just that piece. Now they feel like the class moved along, they got to do a variety of things and they realize that they feel less awkward about a technique or principle by the time they leave... they get a sense of accomplishment.
I many times have a mix of low rank beginners and higher ranking students. Principle or technique of the day works great here too. Everyone starts the same and together. The advanced people get different variations or different aspects to focus on. This even allows you to rotate students, and keep a mix of low and high rank students working together on the same ideas.