I have done these exercises in both 3" heels and in flat jazz shoes (pancake heel).

There are a few exercises that I know of which will definitely assist in flexibility, balance, and strength. I do these exercises before a lesson, and it only takes a few minutes.

#1:
Stand up straight. Flex your knees and ankles towards the floor, keeping your heels on the floor. Bend just a little; these are not deep-knee bends. Hold this position throughout the exercise. Place 100% of your weight on your left foot. Stretch your right leg and point your toes in front of you, then to the side, then to the back. Hold each position for a a few seconds. As you do this, there should be only about 5-10% weight on the moving leg. The less you rely on the floor for balance the better. Bring your right leg back to its original position and change weight from left to right. Repeat with left leg.

#2:
Stand up straight. Flex your knees and ankles towards the floor, keeping your heels on the floor. Keeping your feet together, take your heels off the floor (balancing only on the ball/toes), keeping your knees flexed. Hold for a few seconds. Now, straighten your knees, but don't lock your knees; don't hyperextend. Hold for a few seconds. Slowly lower to a normal standing position. Repeat.

Regards, Hoofer

I would recommed: Pilates, Ballet and Yoga as good workouts to develop some of the strength and flexbility you will need.

There is a big diffrenec between doing these well, with a good instructor, and doing them
without too much benefit and sometimes even danger to your health.

Look for a good teacher first.