Broadway actors seem like they have it easy because they get to work on the big stage and act in front of a live audience. But that is not all it takes to be on the big stage. You have to have a union card, a headshot of your face, and a resume of things you have done as well as a demo reel, which shows what you are able to do. If you are only looking to get into musicals, then you need to make sure that your demo reel contains not only acting bits but musical bits as well so people can see not only your acting ability but your singing one as well. The next thing to know is what type of roles are you looking for. The following roles exist on Broadway: 

Swing: One of the more difficult roles on Broadway is one where you are not necessarily on stage but you are learning lead and ensemble roles. That way, if someone is out the swing can sub in. There are other roles similar to swings, but they are actually on stage. 

Understudy: An understudy is someone who only learns the leads parts and will be on stage at some point throughout the nights of the shows. 

Ensemble: The Ensemble is the group or groups of people that are in the background of a scene or are background singing in the song. 

Principle: The principle of the musicals are the ones that are the leads and get the most lines and do the most in the songs. 

Make sure that you practice the stuff that you are auditioning for a lot and know what you are delivering to the people holding the audition. Also make sure that if your character has an accent that you practice how you deliver that.