If you are a professional dancer, a serious student, or just someone who takes ballet class for fun, it is extremely important to warm up. I think we all know that we should warm up before class, but I have found that many dancers (myself included), don't always take it as seriously as we should.
It's very tempting to just sit in the splits and chat with your friends before class. You might feel loose before class, but you probably aren't warm or prepared for what comes next. I remember when I was still training we would all show up to the school 1-2 hours before class to be dedicated. But now that I look back what did we really do? We listened to music, chatted, and stretched a bit. We may have done a few crunches, but I don't remember us really preparing our bodies.
I think part of the problem is that we didn't really know how to properly warm up. What works for each person is extremely individual and probably changes depending on the day. I personally find what works best for me is to do strengthening exercises that focus on stabilizing my hips and core. It gets my blood circulating and warms up the muscles way before my first plie.
By being consistent with my warm ups I noticed a much faster improvement and less aches and fatigue in my body. I very much encourage you to avoid stretching before class and to instead strengthen and warm your body.
Below is a 5:30 minute video of a warm up I may do before class. I'll continue to post different variations and times in the future and will also include some of the cool down stretches I will do after class or rehearsal. Consult with a doctor before starting any exercise programs.