During the summers when dance classes are not available I look for yoga and pilates classes that focus on core strength and lengthening.  Not to mention there is a lot of overlap between yoga, pilates and ballet and what you learn in one class may help you in another.

This keeps me at least on the same plateau as I was when I left class.

Typically however you can always find a dance class to participate in at some level even during a break.  Tap, Jazz, Modern and Lyrical can all be fun to investigate during a break from ballet class and they keep your body moving.  I have taken Jazz and a Tap class in the past two years, this year I am going to try a modern class during the summer with an intermediate level ballet class.

Also, no matter how advanced you are in a ballet class it is always acceptable and good to take an beginners level class.  IT gets you refocused on the little things that with the faster more advanced technique classes  you tend to over look.

One thing with ballet that is really difficult for me to digest is the faster you move, typically the smaller the steps become and at the same time you start to loose the technique you built upon in eariler classes.  Going back and revisiting gets you reacquainted with these basic movement requirements (which is probably part of my movement problems).

Hope it gives you some insight.