A good dancer is an educated one, so don't abandon school.
Young dancers are training at a very vulnerable time in their lives, through adolescence, and while they are trying to work out who they are as people, never mind as a dancer. So train the whole person, not just the dancer.
I get to the theatre in plenty of time; I prepare my shoes in advance; I eat and drink the right things at the right time. The rest you have to leave to luck!
Body language is a very powerful tool. We had body language before we had speech, and apparently, 80% of what you understand in a conversation is read through the body, not the words.
People often argue about this. Obviously one of the skills in performance is acting, and you can't expect every Romeo to really be in love with their Juliet!
I always recommend a sensible diet, including lots of carbohydrates and avoiding too much fat. Dancers don't need different fuel from other people - they just need more of it because they use more energy.