Your autoethnographic literacy narrative should tell stories of your experiences learning to write that include or are followed by your analysis of both pedagogical method and the social, cultural, and economic circumstances of your schooling.
Analyze the way you were taught and be truthful with the stories even if they contradict (or reinforce) established theories of and approaches to writing pedagogy that we are learning about in our class.
Draw on the strengths of the technology platform you are working with to organize and present your final product.
Your narrative can be inclusive of early pre-school experiences and run up through college to the present. Or, you can focus on a period or periods that you think was crucial. Since you are planning on becoming a secondary school teacher, middle school / high school is obviously an area to consider carefully.
You may be inspired to look back over old pieces you have written, talk to friends, parents, and former teachers as you return in your memory to your experiences with writing. This is a "multigenre" paper; feel free to include samples of your writing or teacher assignments, interviews with teachers, parents or classmates, recreated dialogue, poetic expression/analysis, memories, illustrations, reportage, etc.
One purpose of the exercise is to "know thyself" so that when you draw on your own student experience as you become a teacher of writing you will act in a highly conscious way, making careful choices and recognizing the diversity of the students you will teach.
Your narrative should have an ethnographic dimension. Focus not only on yourself but try to remember/research what was happening to other students in the class or in other classes/tracks or how your social community might have been unlike what others experience (rural/urban/suburban, poor/wealthy/middle class, monoethnic/multicultural, etc.). Exploring the way ability grouping / tracking effected your education is often one of the best ways to look at the influence of social and economic factors on the way you were taught.
I think you could and should write at length on this topic, yet, given the time and expectations of the course, I would consider the equivalent of fifteen double spaced pages a satisfactory minimum length. Of course the final draft should be well-edited, fantastically presented using a new technology platform, and integrate video and additional on-line tools.
Include a diversity of genres, and show that you know these genres well. Genres such as: