I tend to teach my composition and reading classes to a theme. I find that doing so gives shape and guidance to my lectures, which helps me. I find also that it allows students to develop a knowledge base and to work from it, which helps them. It allows them to deal with information that they have already learned, so that they can focus on the application of the knowledge rather than trying to acquire an entirely new set of knowledge every few weeks. Also, it gives them confidence in their own ability to gain and exhibit expertise in a given subject.
Selecting a theme is always a difficult thing for me. Since I will be spending fourteen or fifteen weeks dealing with it, the theme needs to be one that will not bore me. Since I am doing a lot of other work, it has to be something that I either already know or am working with in my own research. And it does, in fact, have to be one that I can have some certainty is accessible to the students--I tried one a semester or two ago that did not work well at all, largely because it called for my students to stretch too far.*
In the spring term, I used genres of music. While there was some initial difficulty, I did get a number of the students on board, and I was able to get in some pretty good papers. It was also fun putting up examples; I think I did a little bit of decent writing, and it is useful to stretch myself a little outside what I normally do.
For the summer, I am returning to my own literary work (though not exclusively, as should become evident). It is a truism that a hero cannot be any better than the opposition that hero faces. Antagonists, then, drive the plots of stories--whether in writing, on stage, on screen (big or small), in games, or whatever. And it is the antagonist, in any of a number of forms, that is the theme for my composition courses in the summer term.
*I tend to adhere to Vygotsky's concept of the "zone of proximal development," which is that level of difficulty just beyond what a student can do unaided. It provides a comfortable stretch for the students' abilities, challenging them to improve without being so far ahead of where they are as to promote disengagement because "there's just no way I can do it." Sometimes, though, I do miss.