What main elements of "The Way To Rainy Mountain" by N. Scott Momaday could focus on if I were to make a presentation about it?

My suggestion would be that you do your presentation on the organization of The Way to Rainy Mountain so that your fellow students can better understand it. Of course, organization also has to do with language (which is Momaday's true subject matter here). 

For example, you could begin by discussing the three major parts of the work, how they are important, and how they are in themselves examples of parallelism: "The Setting Out," "The Going...

My suggestion would be that you do your presentation on the organization of The Way to Rainy Mountain so that your fellow students can better understand it. Of course, organization also has to do with language (which is Momaday's true subject matter here). 

For example, you could begin by discussing the three major parts of the work, how they are important, and how they are in themselves examples of parallelism: "The Setting Out," "The Going On," and "The Closing In." Each of the major parts in The Way to Rainy Mountain is further divided further into twenty-four numbered sections. Each of those sections is further divided into three voices: one about myth, one about history, and one about personal experience.

It is through these voices that Momaday tells the Kiowa story through language. You can connect language with the Kiowa tribe with this quotation:

A word has power in and of itself. It comes from nothing into sound and meaning; it gives origin to all things.

If you choose to go further into the story than the organization and its importance to language and the Kiowa tribe, you could talk a lot about Momaday's own grandmother, Aho, who experienced many of the tribal rituals. A dramatic interpretation of one of these rituals might be an interesting way to begin or to end your presentation.