I've had the opportunity to visit several colleagues' classes this semester. It was a privilege for me to sit in on a variety of different disciplines that are not my direct area of expertise across the humanities, natural sciences, and social sciences.
I've volunteered to serve as a peer mentor, which means I sit in on another professor's class to help him or her think about the teaching and learning happening there. There are a small team of us who are doing this. We began by visiting each others' classes and practicing some techniques for providing feedback. We explored different things we can look for, such as tracking the level of questions being asked, mapping the interactions taking place, capturing student engagement (check out their body English--it speaks!), or even just the gestalt "what's-it-like-being-in-this-class?" from an outsider's perspective.