Do your own pose, do not compare with your neighbor
For most of us the mind tends to overrule the body. So, if the person next to you gets her face all the way down to her shins in “Forward bend”, you naturally want to get there, too, no matter how much your hamstrings hurt.
The only right way to practice a pose is to feel the stretching in the right place, instead of trying to force yourself into your neighbours’ pose. Yoga is not about comparing with someone on a mat next to you - it's about doing the right thing, to improve flexibility in your body. If you are not sure, if you're doing all right, always ask your instructor before or after the class.
The purpose of each pose is to learn about your own abilities. How strong is your left and right side? Which leg or shoulder is more flexible? Etc. It's all about exploring yourself and learn your stronger and weakest points, to know how to work balance in your body.In particular, please don't compare yourself with your instructor, who has probably many year of practice on her/his mat.
Going to yoga class - focus on your own space - your mat. Listen to your breaths, link with every move and simply enjoy the experience.