When I used to teach multiple classes a week – for a time up to 14 each week! – I always had clients coming up to me stating they would like to be in a class but didn’t know what / how to enter and fit in.
Here’s the basics. First, come a little early and let the instructor know you are new. This way they can help you know what equipment you need to have for the day, how to use it, and ask about any injuries or modification you may need.
Second, find a spot where you have enough room to move and can easily see the instructor. I know beginners like to be in the back row, however if you can’t see and you spend the whole class craning to look around a regular you aren’t going to get the best workout and your experience may be less enjoyable or not feel worth the effort and nervousness.
Third, pick a class that interests you and/or bring a friend. Having a buddy can really help take the feeling of being the newbie away. Fourth, have a good time. The point of group exercise classes is to have fun, not necessarily to be the best dancer or have the most flexible body or lift the most weight/do the most reps. If those were to goals you would be in what we call “training” not group exercise “class”.
And very last – don’t let your fear of looking silly or being a greenhorn in the room stop you from trying out something new. We need new and challenging activities not just for our bodies but also for our minds. Who knows the “class” you thought was interesting may become something you enter into “training” for.