Don't hide in the back of the room when you're new. Yoga is nothing like that algebra class of your nightmares. You won't be called on if you plant yourself in the front, and it's the best spot to see the teacher.
Leave your sermon at the door. When a person walks into a yoga class, they expect to do yoga. Be careful with your words. Your beliefs are your opinions. Your opinions are your judgments. Judgments do not belong in the yoga room.
Using the physical body as the main component of a spiritual practice is newly popular and barely existed just a few decades ago. Prior to that, asana was viewed as a single limb on a larger tree, mostly used as a way to get the body ready to sit in meditation for a long time without distraction.
When it's getting close to the end of class and it is time to stretch, please do not decide that in lieu of stretching you'd like to do arm balances that cause you to flop all over and fall on your neighbors who are in pigeon pose.
Every yoga teacher I've ever had would balk at my confession -- adding a little friendly competition to my yoga has made me more invested in my practice. I will savasana better than you! I will ujjayi breath better than you! I will fall out of headstand better than you!
Yoga is more than just stretching and relaxation. Daily yoga practice includes a comprehensive system that builds strength in the body and mind. There are some key postures that helped me access the deep reservoir of inner fortitude that every person contains within.
I made an assumption that being competitive with other people drove me to be better, but in actuality it distracted me from focusing on my own process. When I compared myself to others I wasn't honoring my own path.