* If you are serious about a career, DON'T get involved in your school theatre department. Go found a professional teacher and start taking lessons. Ignore this if your school is winning REAL regional or national awards and not B.S. ones. Google them if you aren't sure. You don't need the politics or self-importance of most H.S. programs. Some have success from there, but more have overcome their high school careers to succeed.
* Do not get an agent until your teacher tells you that you are ready for one.
* Do not pay in advance for anyone who says they can get you bookings. Anyone doing that is a scam artist. Real agents only get paid if you work. Teachers are a different story. They get paid every time you have a lesson.
* If you want to be in musicals, work out. A lot. Being able to sing while Broadway dancing is HARD. This is true even if you are a character actor. You don't have to be a matinee idol, but you have to have the lungs of one.
* Don't decide on what you want too early. See what you are good at. Work your skills and see where your natural talent is. Trust your teacher even if she says things you don't like. Especially if she says things you don't like.
Hope this helps. Break a leg!
So you want to look at two things
Who do I know ? Or my friends know ?
This could open a door to an audition and potentially a booking.
Getting qualified and educated in the field of acting to push the process faster. As this makes Networking so much more fruitful if your line of network has no connection to the entertainment industry.