One aspect is nutrition. One dancer may function just fine after she eats a banana for breakfast, but maybe you need to eat a bowl of oatmeal with a spoonful of sugar, raisins, and a glass of milk. Maybe you need eggs and bacon. One dancer never eats chocolate before she dances because she claims that it causes her muscles to have less stretch. No one can tell you what's right for your body, because only you know. But that's another problem - how do you know?
- keep a food diary - write down the foods you eat every meal for a week or two and observe how you feel one, two, and three hours after. Were you more ready to warm up and stretch after you ate a full meal or with just a small snack? Did more protein or more carbs or more veggies/fruits help you to keep your energy up? What kept you fuller for the longest period of time? What times of the day were best for you to eat?
- observe and make changes - if you don't keep the diary, observe how you feel from day to day or meal to meal. I realized that I feel much fuller for much longer if I include a fruit or vegetable at every meal (usually both at lunch) and carry a baggie of almonds with me (a handful of almonds can hold me for an hour).
- bring an extra shirt - one for warm up, one for the rest of class. A boy in my class does this every day, and I used to think it was silly until I realized how chilly my skin got when we started learning the combinations.
- bring a sweat towel - for ballet, mostly, when you can't just change your leotard. Keep a towel with you at the barre to prevent sweat from drying (can also help prevent breakouts).
- wear pants and jackets for warm up, or put them back on when you get cold - I didn't notice how important this one was until I got to 18. When I was 16, I could plop into the splits regardless of where I was or what I was doing. And now, it's even worse - starting class in booty shorts and a sports bra is really hard for me. I always have a pair of jazz pants or sweats with me to keep my hamstrings from pulling.