I teach a Korean Martial Art (Tang Soo Do) for a decidedly American audience. I do actually have a native Korean in class who politely never corrects what I am sure is a butchering of her language - but "Kor-English" is a topic for another day. For my American students, I have a pattern that I follow for class that seems to work.
We always begin with stretches from hand to head to foot, making sure that all muscle groups are properly prepared before any rigor is added to the session. Then the first 30 minutes (each class is an hour long) is very aerobic in nature. We work on stances, blocking and striking techniques, stretching and kicking. This is done is a fairly fast-past sequence with no real breaks.
I've seen (even in my own school) instructors who will have the class do a single technique, with maybe ten reps, and then "parrow" (take a break to adjust their uniforms) and catch their breath. Now, don't get me wrong - I'm not a Drill Sargent looking to see how many neophytes I can drop (well, maybe red and black belts), but I do want to see everyone breaking a sweat and pushing themselves to greater strength and endurance.
There is something about trying to perfect a strike, a block, a stance, or other technique when the body is tired that cements the physical movements into the body. It also has the added benefit of teaching the student that they can still perform even when they are tired. This alone could save their life in a real confrontation.
Once I've achieved a level of physical exertion (some say exhaustion), I then move the class into less rigorous activities such as Hyung (forms/patterns/kata) - but make no mistake, this is not a time to relax, as I expect sharp movements, low stances, good balance, precise movements, and powerful techniques. During all of the aerobic and anaerobic exercise the students must always respond with appropriate etiquette and confidence.
I always try to end the class with a skill builder that is also fun. This could be bag work, team or partner-based activities or working on something new. At the end of the class the students feel they have had a great workout (very important to our clientele) and they've had an enjoyable time. As I said earlier, I'm not trying to build a military platoon here - we're keeping people in shape while giving them a very useful skill.