I agree about the yoga. I had a very sore back about four years ago, but four years of going to yoga class with my wife has eliminated that problem entirely. The only stretching I do before dancing would be to make sure my Achilles tendons are stretched a little. My wife is a fitness instructor and she recommends lying on your stomach and lifting a leg and the opposite arm and then switch sides. Lift your head slightly. After a few times on each, try lifting both legs and arms at same time and hold it. She claims it is a good leg and abdomen stretch. As for the abs, she likes a situp in which you are on your back and your legs pointing straight up in the air. Have your hands stretched out above your head, on the ground, then lift your arms and try to touch your toes (or ankles) of your legs that are straight up. Don't lunge your neck or back, try to keep everything in solid frame (like dancing).