i teach in Malvern, PA, at a yoga center and a number of gyms. i have not found my students getting bored in any of the classes, but that may be because they are vinyasa classes.
When i teach, i spend time talking about the asanas and correct allignment, pranayama (indicating inhales and exhales), dristi, where to take the mental focus (for that day) and why. I make certain that we do a variety of poses each day to work the body in every way imaginable: warrior series, uttkatasana series, triangle series, balancing series, back bends, abdominal work (such as navasana), hip openers and forward bends. I'll also discuss principles of living (yamas and niyamas) as well as various meditation techniques during class.
So, for example, while they are holding warroir 1 for 5 breaths, i may discussion proper foot alignment and how the legs should feel (the deep opening in the legs and hips), particularly if it is a class with many beginners. If it is a more experienced class, i may speak about how asana teaches various lessons of the yamas and niyamas--for example, how being present in the pose without seeking or expecting "perfection" helps us with aparigraha (non hoarding). I may even do a pranayama meditation, hardly even mentioning the asanas. Or, even a chakra meditation.
Part of this is to keep their attention in the present--focusing on my voice can do that. And as long as i feed their minds (which are open via the attention that they give to my voice) on things of grace and beauty (which of course i strive to nourish my own mind and heart with this), then we are in a good relationship of group learning. Their attention moves to my voice, fostering focus and eventually leading to awareness of the asana and deeper. Also, they get various teachings in the yoga tradition, which deepens their understanding of why they are doing what they are doing.
in my classes, students do repeat the same poses over and over, because that is how one learns the asanas. I often tell them that there is always somewhere to grow into, so to stay present in the pose and with the breath. The most important part is not the asana, but being present, and i encourage them to practice that most of all. In order to develope attentiveness, i may change the sequence of the postures every few classes, or i may add a new one in and take another out.
Charlie is right as well. you need to stick to what you know and love about yoga (your truth). this will guide your teaching.
if you'd like to visit one of my classes, you are more than welcome to do so. I work at Power Yoga Works in Malvern, PA. I generally teach on Monday, Wed, and Thurs at 7:15 pm (Basics classes) and on Tues and Thurs at 9:30 am (All levels). I would be happy to meet you and discuss these concerns in person as well. :)
