I have looked into this quite a bit as I've been an aspiring actress my whole life! LOL
First, I would suggest that you look into organizations like S.A.G. ( http://www.sag.org/ ). Then I would recommend looking for an agent. You can generally go to Google and type in 'Talent Agencies in ____________'.
I would also recommend that you invest in an 8X10 head shot that you can easily screen your resume on the back.
It's not easy to get in, but you can do it! XD