One of the best things to know ahead of time is what your administrators look for in an observation. Every school and every administrator is a bit different, but this article compiles interviews with principals from various levels and areas and asks what they look for, both from tenured and non-tenured teachers. It's a good companion to your school's or district's observation rubric so that you know what to expect your administrator to look for.
Another common practice I've seen in schools is the peer observation. I know the first time I did a peer observation, I was a bit confused as to what I was supposed to look for, so I ended up scrutinizing everything and getting information overload when it came time to debrief. The learning-centric method that the teacher in the video models is a great one, because it not only primes us as teachers to look for it in our own classroom, but it gives us a focal point for our observations.
This article comes from a veteran teacher, and it really captures what preparation can and can't be done for observations (and the frustration of having a walkthrough happen right after you stop doing something interesting!). There are lots of good ideas about preparing the students and handling anything unexpected here, which can definitely ease the nerves before an observation.
This article primarily aims itself at new teachers, but there are some useful tips for not only getting through an observation, but also getting feedback on something you know you're not comfortable with before it hurts in a future observation. The questions on the side for new teachers and mentors are also really helpful if you find yourself in one of these roles with the need to reflect.
A set of tips is aimed at UK teacher candidates, but has some helpful tips about preparation ahead of time and working around such nasty chance occurrences as technical difficulties and bugs in the room. Some of the tips feel obvious, but there's a lot that they've thought about ahead of time so that you don't have to.
I love that this article not only lays out the best practices for handling observation feedback, but it puts it in the framework of Marzano's philosophy. Whether you love or hate Marzano, many schools have adopted his work, so it's not only good to know how to use feedback to set goals and improve, but also to have this framework so that you can show your school that you are aligned with educational best practices in the wake of a bad observation.
A story that is on the lighter side of things, but it tells the tale of an absolutely unplanned personal problem in the middle of an observation: the teacher's pants ripped. Nearly ten years later, the teacher has reflected on it and used it to remember to lighten up and prepare for anything as a teacher, and as a trainer for student teachers, he uses this story as a gentle reminder that sometimes you won't be able to control everything.
This is actually a forum post on a site for teachers, but it's a valuable read because it captures some of the doubts and feelings you may feel (even if your observation doesn't go as poorly as you thought) and walks you through recovering from the blow. The teachers supporting the post have some good advice, and they also give teachers a good reminder: even if you feel bad, you're not alone.