DO arrive early. If you can, try to get to class a couple minutes early. I realize sometimes life gets in the way and traffic and/or public transportation is slow. However, it is nice to get on your mat with a few minutes to spare so that you can mentally and not just physically "land." Lie down, close your eyes, stretch, breathe, and just get ready to practice.
DON'T eat for two or three hours before class. If you practice yoga on a full stomach, you might experience cramps, nausea, or vomiting, especially in twists, deep forward bends, and inversions. Digesting food also takes energy that can make you lethargic.
DO let your teacher know about an injury or condition. Most teachers go around the class and physically adjust students to help with their alignment or deepen poses, so it's important they know about injuries so they can steer clear of that area on your body. Also, teachers can show you modifications and can cater around your injury to help you get the most out of the class even if you are injured.
DON'T get distracted by others around you. Yoga is not meant to be competitive and it is unimportant if the person in front of you can hold a handstand for 5 minutes. Practice pratayahara, or withrawal of the senses. Focus on yourself and the way your own body and mind feel.
DO create an intention. Your intention does not need to be super deep or spiritual. It is just refreshing to realize a reason that you made it to your mat. Whether it's to gain balance, strength, flexibility, or just peace of mind, let your intention fuel your practice and you will feel more connected to the practice as a whole.
DO put your cell phone on silent, for obvious reasons.
DO be quiet. It is fun to take class with friends, and it's okay to have an occasional whisper, but keep most conversation to a minimum so that you don't distract neighboring participants.
DO bring a towel and your own mat, unless the studio has mats available to rent or borrow.
DON'T push it. Try to listen to your body and rest when needed. Yoga is about figuring out your edges, not pushing past them. If you are new to yoga, you probably aren't going to be able to do every pose instantly. Understand that yoga is called a practice for the reason that the more you do it, the more comfortable you get. Patience is key.
DON'T enter class late or leave early; or at least try not to. Classes are taught in a manner that physically and mentally make sense. You will get the most benefit when you are able to experience the whole class.
DO approach your practice with an open mind and open heart. It's just yoga!