Ballet is hard.  I've been doing it for twelve years now and here are a few guidelines that are good to follow in general for ballet.  These are not in any particular order, but here we go.
1) Work harder than you ever have.  Don't come to class lazy, come to class ready to learn.  Or don't go to class at all.  (Yes I know that sounds rude and brutal, but trust me in this one)
2) Take corrections well, when your teacher corrects you, don't take it personally, and try to keep applying the correction.  Keep your cool and keep in mind your teacher is just trying to help you improve.
3) Show up early to class and come properly dressed and with your hair up.
4) Work on your weaknesses outside of class.  Don't just come to class expecting to improve without at least a little work, stretching and or strengthening outside of class.
5) Don't be afraid to ask questions. 
Anyways, I think that should be it, or at least all I can think of off the top of my head.  Have a great day and just keep dancing!! ~Mia