YOGA ETIQUETTE

New to Yoga?  Get the lowdown on courteous conduct before you head to class.
Arrive early.  Getting to class about 10 minutes early can help you settle in and align your attitude with the purpose of the class.  Wait for the teacher's permission to enter the room.  While you are waiting, you can practice a pose, do a few stretches, or just sit or lie quietly, breathe and get centered.    Although arriving a few minutes late is better than skipping the whole practice, you need to rethink if you are chronically tardy.  Arriving late often shows disrespect to the teacher and the other students, and it robs you of the chance to experience the full benefits of the class.  If you are late, enter the room quietly.  If you need to leave class early, let the teacher know ahead of time, and choose a spot in the back of the class.
Create an intention.  To help focus, you might find it helpful to dedicate your practice to a certain intention.  This might be to become more aware and understanding, more loving and compassionate, or healthier, stronger, and more skillful.  Or it might be for the benefit of a friend, a cause - or even yourself.
Dress for yoga.  Wear comfortable and non-restrictive workout clothes.  Wear pants, shorts, and shirts that are form fitting rather than baggy.  Choose a shirt than can be tucked in or one that is form fitting.  Select pants or shorts that all you to move comfortably and fit well.  No special footgear is required, as you will be barefoot.  Consider leaving jewelry at home.
Find the Quiet.  Turn off cell phones.  If you are on call, please leave it on vibrate so that the peace of the practice is not disturbed.  Save enthusiastic sound effects for your home practice and limit socializing with friends to before and after class.  It is great to share a class with people you know, but it can be distracting to yourself and others to have an extended conversation during the practice. Be respectful and considerate of the  other student's practice.   
Injuries.  Be sure to let your teacher know of any injuries or relevant medical information and definitely sound an alert if you feel pain in any pose.  Do not hog the teacher.  Resist the temptation to ask for an adjustment in every pose.  Instead of regaling everyone with a blow-by-blow account of your injuries, see if you can incorporate the yogic discipline of restraint into your practice.  Come early or stay late to talk with your teacher or discuss specific issues.  Better yet, schedule a private session to fine-tune the asanas to suit your particular condition.  Do not push yourself to the extent of pain, in any pose.  Challenging yourself in a pose is different than pushing yourself to injury.  If you are injured or tired, skip poses you can't or shouldn't do, or try a modified version. 
It's your practice.  Instead of trying to go as deeply or completely into a pose as other might be able to do, do what you can without straining or injuring yourself (ahimsa/non-violence).  You will go farther faster if you take a loving attitude toward yourself and work from where you are, not from where you think you should be.  If something does not make sense to you, please ask questions.
Practice saucha (cleanliness).  Bring a towel if you sweat a lot, and arrive clean and free of scents.  Such products can be difficult for people with allergies.  Wearing lotion to class can cause your hands and feet to slip on your mat.
Allow 2 hours between your last meal and class.  If you practice yoga on a full stomach, you might experience cramps, nausea, or vomiting, especially in twists, deep forward bends, and inversions.  Also, food also takes energy that can make you lethargic.  Also, please no chewing gum in class, as choking is a probability.
Drink water before and after class.  In yoga, we typically don't drink water during the practice since its purpose is to heat the body up, not cool it down.  We can also use this action as a way to avoid a certain pose or feeling.  Of course, if you need to, please drink water.  Always keep yourself hydrated.
Sticky mat.  Bring your own mat.  Having your own personal mat is more hygienic.  You can purchase them from a local retailer or off the internet. 
Shoes.  Please remove your shoes while walking around the studio.  Be courteous of your neighbors mat, by stepping over it.  If you are doing partner work, it is courteous to ask, "May I stand on your mat?" before jumping feet first into your partner's yoga sanctuary.
Stay for Savasana.  As everyone settles in for a long Savasana (the ending of your yoga practice where body and mind balance), you may feel like sneaking out.  Relax and stay put.  Aside from distracting the other students and showing disrespect to the teacher, you will miss the deep relaxation. 
Reflect afterwards to think about what you did in class, so you can retain what you learned.  Review the poses you practiced, and not any instructions that particularly made sense.  Even if you remember just one thing from each class, you'll soon have a lot of information that can deepen your own personal practice.
Yoga is a sacred space - a time and place to go inside, be a little raw, retreat from the world. 
(Text borrowed from Nora Plonsky and Yoga Journal)