One of the most important things you have to do when starting out an acting career is make sure that you get your headshot to the right people - casting directors. Your headshot acts as your business card; it's the first thing casters look at when they choose someone to play a role.
The most efficient way to get your headshot out there is to get an agent. Do a Google search for reputable agencies that operate in your area, or in areas you're comfortable going to, and get their contact information. You can also find agencies in phone books and in materials found in the performing arts section of your local bookstore. Then, send your headshot, along with a cover letter, resume, and contact information, to as many agencies as you can. The more agencies you send out to, the more chances you have of one replying positively. Just make sure you do your research on each agency - you don't want to fall victim to a scammer.
It's also very important to pick a reputable agent, as some casting directors limit auditions to a few agencies. They have to go through thousands upon thousands of headshots and resumes, so it's understandable why they'd like to streamline the flow of paper that comes their way.
Once you've signed with an agent, you can sit back and let him do the work for you. He'll send your information to any and all jobs that you qualify for. You'll also get tips on improving your headshots and how to make your resume more appealing to casting directors. Once your agent lands you an audition, you'll need to bring more headshots with you. The preferred size is 8x10; some casting directors have been known to toss away headshots that are smaller.
If you can't wait for an agent to get back to you, or can't afford one, there are still some ways you can get your headshots to casting directors. Publications like Hollywood Reporter often have information on open call auditions, in which interested individuals don't need the services of an agent to audition. Again, you can also do a Google search for any open calls in your area. Websites such as castingnetworks allow members to upload their profiles for a fee. These sites will automatically let you know when an open call applicable to your profile happens. In certain cases, you'll be able to submit your profile electronically.
Electronic submission has an added perk - there's no limit to the number of pictures in your profile. That means you can have a different shot for every look, and submit an appropriate one to the casting agent. If the audition calls for a father figure, send in that photo of yourself in a golf sweater and glasses.
Of course, it's always best to bring a few 8x10 headshots to the audition, no matter how you got there in the first place. It shows professionalism, and you'll be ready in case the casting director asks for extras. Good luck breaking into acting!