Who: teacher; students (number, gender, ethnicity, age); aides
What: class activities/assignments; context of work within course
When: day, date, time of observation
Where: classroom environment
How: routines and mechanisms of the classroom (how the lesson functioned); effectiveness of chosen activities and assignments (how well the lesson functioned--from your perspective, the students' perspectives, etc.)
Why: objective(s) of the activities/assignments, whether explicit or inferred
Second, I want you to think about what effect this observation had on you as a prospective English teacher. What thing(s) did you notice that have made you think since doing the observation? How does that thing affect the way you think about the profession of teaching English? The "things" you might have noticed include (but are not limited to) a specific student, a teaching practice, an attitude displayed, a classroom management technique, specific behaviors displayed by students and/or teacher, the subject matter being taught, etc.
Second warning: Don't assume that the two things I'm asking you to address in the paper are implying a specific kind of structure. That is, I don't expect that the paper will have a "part one" that talks about the class and a "part two" that analyzes it (although this is a possible structure). Just write the paper so that it includes both what you observed and how it impacted you as a preservice teacher; the way you combine those elements is up to you.
Good luck with it. Come by and see me if you have questions or want
me to read over a draft.