I find that the composer and sound design community is one of the most supportive I have seen in the music world. Get engaged in that community and you will find everything you need.
Your music and compositional skills may get you your first gig, but how professional you are: how good you are to work with will get you your second (and third, and fourth....) one and make or break your career. Be professional.
Don’t try to be the next Hans Zimmer or John Williams and try to sound like them. Hans Zimmer is already the best at being Hans Zimmer, and John Williams is the best at being John Williams.
It's important that you can do what you say you are going to do, so try not to oversell yourself if you've no chance of delivering on it as it will come back to bite you later!
Every project should be a learning experience, whether it is good or bad. I had a client who had nothing bad to say about a piece I wrote and I was blown away.
Composing for media is a high pressure job. It requires creativity on demand, on somebody else's deadline, and you need to make it sound as near to perfection as possible.
Don’t be afraid to say no to a project if it does not make sense to you. Follow your instinct. You may end up in a limbo on a bad project with random people.