Once an aspiring actor has a good resume, he or she is ready to begin to work for a career. While building your resume and until you are well established as a professional actor, you need to network. My article on Networking for Success explains how to do that. Networking includes fishing for a agent. I call it fishing because that is exactly how the process of getting an agent works – just like angling for a fish.
The aspiring actor needs to find an agency within a couple hours of where he or she lives. Agents do not sign people who live out of state or at a far distance from the agency. Then you need to submit for representation according to the instructions given on the agency web site. Of course, you are wary of scams as described in my book, The Tao of Acting. Feel free to contact me anytime to check the validity of an agency. You need a good head shot, resume and cover letter. (see How to Write a Resume, etc on my website). You will be sending these things to the agency. Occasionally, an agency will have an open audition at a specified day each week or month and you can take your things and attend one of those.
Do not start looking for an agent before you are ready. It isn’t true that getting an agent is the first thing you need to do to become an actor. It usually is the last thing. First you need to be an actor, working in amateur plays and films, taking an occasional class and building a strong resume that is proof that you can make money for an agent. Trying to get an agent before you are ready just will disappoint you.
For more information about agents and how the work go to http://talentagents.blogspot.com. It is a good source.