Before you have to sign up with a union, turning down roles is a bad idea. You never know who the next person who is going to blow up is.
You just sign up, a lot of actors have acting programs
Acting schools in LA are useful because they help with networking. Even if you've done a school somewhere - it's still worth it to keep going. Keep improving, meeting people.
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Being a working actor is hard
But if its the kind of thing you are interested in, and good at, I think it's worth it.
Like imagine this: going to another country to chase a dream you've had since you were a child, leaving your home and family, looking for an acting school
If you're in HS, and you currently have your parents taking care of you. Make as much use of their resources as you can, cause you won't have them in a bit.