An exercise you can do that's taught in both jazz and ballet, is to lay on your back, without arching (but so you could slip your hand beneath your back and the floor), with your tailbone and shoulder blades not pressed, but relaxed against the floor; take your leg and lift it straight in the air as close to your body as possible without tucking your hips or changing the orientation of your back. Hold for a few seconds, release; repeat 4 times; hold for 8 seconds, point your toes (do not sickle the foot); repeat 4 times; hold for 8 seconds, flex your foot (your hamstring will be sore, you need to keep the leg straight); repeat 4 times. Do this for both legs, and once a day, every other day, with proper breathing - pull into position, inhale, extend to exhale.
You can do this exercise turned out as well, which will improve your sau-de-chas and grand jetes.[/i]