How to improve one's extention? [for dance]?

You have to work on your theigh muscles. Some great exercises are ones where you get down on all fours and slowly lift one leg up "peeing dog" style do 20 then do the other side then do 20 more and the other side again you can do more things like putting your leg out to the side "peeing dog" style again then extending it straight out bringing it back in then down. Just work on it everyday.