How to stay successful in the musical theatre world?

Hey I was just wanting to know what musical theatre courses do you think are worth auditioning for? Also can you tell me after you've done a course and you're ready to get an agent - how do you know how to get one let alone a good one? And once you go into the business i know this sounds stupid but how do you keep yourself employed other than having an agent? If you have any stories or advice please do share your comments. Thankyou and please reply if you can.