You can start thinking about this by making a note of your technical weaknesses.
Every student knows what their most common correction is.
You can probably put aside 15-20 minutes a day to address a few exercises that use the muscles involved in your ballet class corrections.
There are also a few exercises to add for almost anyone.
Foot exercises, especially if you are doing pointe work, are a good choice to do every day.
Using a stretchy band both under the toes (for lengthening/pointing) and over the toes (for flexing) is a good one.
Toe swapping, 'playing the piano' and pulling a towel are good too.
The shin splints and sore calves that show up after returning from a break are from loss of strength in the foot muscles.
Three very slow motion pull ups for your abs are all you need to do per day.
Starting lying on your back with your knees bent, feet flat on the floor, pull up slowly with your lower ab muscles.
Count to 10, for moving up to your highest point.
Your shoulders and shoulder blades will be off the floor.
Then slowly down, but don't rest.
Stop an inch from the floor and start up again.
Put one hand behind your head if your neck is straining.
Choose a couple of stretches - your tighter areas.
Stretch gently because you are not going to be as warm as a class will warm you up.
If you're skiing, swimming, rock climbing or doing some other sport, stretch afterwards.
Have a great break!