I have the same problem and ballet exercises help me a lot. Do lots of workouts that focus on the feet and legs, especially moves like the plie, tendu, and degage. Basic ballet foot stretches are also beneficial. I'm sure you can find videos on YouTube to help guide you, too.
I've also noticed that yoga helps me with these issues, especially moves like downward dog and the tree pose.
Stand on stairs with your toes and let your heels stretch downward
Id buy a Bosu ball. It is a half shaped ball and it is use for balance and strengthening exercises.