Observations are a great way to improve your skills as a teacher. It's so much easier to see what's happening (and analyze the successes and failures) when you aren't at the front of the classroom and responsible for giving students the skills to walk away using today's target language correctly.
That said, you have to know on which points you want to focus when observing a lesson. Is it teacher talk time and/or student talk time? Is it the lesson structure? Is it how the teacher sets up the activities to practice and reinforce the material? If you just walk into a class as a passive observer, you'll learn a trick or two... but that's about all.
Whenever I do an observation (and I do a lot), I always watch and comment on the following:
1. How is the lesson structured? Is there a warm-up? Does the grammar, vocab, and other target language get introduced effectively? How do the activities, worksheets, etc. allow the students to practice the material?
2. How much time is devoted to pair work and group work? Or is it a teacher-centered class that gives students little chance to use the language?
3. What is the teacher's attitude in the class? Is it friendly? Is it positive? Is it patient? Does he encourage the students to relax, not worry so much about producing perfect language, but rather communication?
4. How much does the teacher talk? Is it effective (giving clear instructions, examples, etc.), or is it ineffective (too many anecdotes, jokes, slang, speaking above or below the level of students, etc.)?
5. How much do the students talk? This may be there only chance in the week to use English, so they need to practice as much as possible.
There's a lot more to look for, but if a teacher hits most of the above points effectively, the class is usually a success.
Chris Cotter
www.headsupenglish.com