I am an actor and a photographer.  Which comes first depends entirely on the day!  I love working with fellow actors to get the best possible head shot for them.  As a working actor myself, I have a unique insight as to what agents and casting directors are looking for in a headshot.  Your headshot is your calling card and gets you in the door for everything from auditions to meetings with prospective agents; don't trust them to just anyone.  Get to know your photographer, that's the best piece of advice I can give.
 
Cheers,
Joe