Excerpts from  Actorschecklist.com

• Generally, the casting director can be thought of as a prescreener. In the end, directors, writers and producers make the final decisions on who to hire. Naturally, there can be exceptions to this.
  

• Among the sources that agents tap for actors are: agents they know, to a lesser degree agents they don’t know, managers, their own files of headshots, personal recommendations, actors they have seen perform in various venues like stage.
  

• Casting directors will look at your photo and resume and then ask you to read. If they like the reading they will then go ahead and schedule a time for you to come back and audition for the producers and director.
  

• Casting directors use a combination of intuition and experience to send candidates onto call-back auditions with producers and directors. Many casting directors were actors early in their careers; others were stage managers, and/or assistants to various producers or casting directors before moving into casting themselves.
  

• Some casting directors work in-house, but nowadays many are freelance hires with their own businesses that have to be licensed.
  

• Once the director and producers have decided which actors they want to hire, the casting director is the one who then negotiates money, schedules and billing with the actors or their agents.
  

• Since they want you to do your best, which in turn reflects well on their job performance, casting directors have been known to impart subtle signals, helpful hints and conventional wisdom while escorting a prospect into a reading. Therefore pay close attention to what they might have to say.

Excerpts from  Acting Workshop On-Line  

• Don't just wait for agents to respond to your mailings.  Market yourself directly.  Contact your nearest  AFTRA/SAG  office to see if they have any casting director contact names and addresses.  Watch TV commercials for your local businesses.  Call the various businesses and ask who do their TV ads. Then call the ad agencies and ask if they keep actor files and/or who handles casting for their productions.  

• Contact big companies directly. Some companies do some of their own productions in-house and keep actor files. Also ask who they use for their outside production work and which agencies they use for casting.

• Contact your local production houses.  Often times the production houses do their own casting instead of going through agencies.  

• Contact your local film schools or universities with film making departments.  Find out who is making student films and make sure each of those aspiring directors know you are an eager actor willing to work (expect to get NO pay.  But you might get a video of the films you are in - from which you can put together an audition video to send to agents).

• Check your local papers, film commissions or trade publications for audition notices for independent films that might be filmed in your area.