I am having a difficult time finding anything on the Internet about how to teach John Phillip Sousa. I can find biographical information, but not many teaching ideas.
If the basic concept is for introduction, I think that it might be really fun to open a lesson on Sousa by simply listening to his music. Pick some of your favorite marches by Sousa. Four would be good, to start. Have kids divide a sheet of paper by folding it into fours. For each quadrant, write the name of the march on the board, ask them to write it down in a box, and then simply have them listen to the music. As they listen to the specific march, ask them to jot down what they note or experience. I would make sure you have a good system to hear the music on and let it project so the kids really "feel" the march element. What does it sound like? If they have heard the music before, write down where they have heard it. What musical instruments do they hear? What is the rhythm? What might be the purpose of the music? Is it in a minor or major chord? Have kids jot down these ideas as they listen to each march. Then, after the four are done, go ahead and jot down on the board what they say and simply discuss their findings. As they discuss, you might be able to add some overarching ideas to the study of Sousa. This lesson does two things. The first is that it introduces the students to the music of Sousa in an open manner. The second is that you start "talking" about the music of Sousa, which is the end goal of the lesson, I presume. In this, an introductory lesson can serve as a launchboard to further study.