Be sure to go slow. For some, this will be new to them and for others, they will know quite a bit. So, go slow so no one feels left out. If ripping needs to be done, it's always nice when the teacher does it for you. When you are new, ripping is frustrating and if the teacher does it, she can whip it out in no time and you don't feel so bad.
If you see someone struggling, ask them what they don't understand. Some times, someone doesn't understand part of the process but is afraid to say so out loud, so look around and keep an eye on progress. Some classes I get frustrated if I don't understand part of it, but don't want to have to ask about it if everyone else seems to understand.
Be friendly. Be very open to everyone. I've had teachers who would help me iron even if I was behind (making purses, OMG) and it really helped me catch up to the rest of the class. I found out I don't care to make purses anymore. I like teachers who explain a section at a time and then let us do that part before telling us the next step. Taking it step by step. I'm talking beginner's quilting classes. For newbies.