Practice your craft. Take acting classes, such as improv, commercial, theater, and TV acting classes, in order to be a well-rounded actor.
Make sure you have a great headshot. Find recommendations for photographers who take good acting headshots. Ask the other actors in your acting classes or research acting forums online.
Look for jobs constantly and apply. Join online acting sites, such as LACasting.com. Check out Craigslist for acting gigs as well. Send your resume and headshot to all the agents who are looking for your type. Apply for student films and independent films, which will help you build your resume.
Practice your lines repeatedly until you have them memorized. Tape paper over the other character's lines, except for the first few words. This helps you to listen and react better. Write down your lines to help you memorize them. Ask friends or family to help you with your lines.
Know what you are going to wear the night before. Follow the clothing instructions they gave you, if any. Dress for the role or dress in a nice, presentable manner. Don't wear red, white, or black, as they doesn't show up well on camera.
Arrive to the audition location early to find parking, sign-in and read your lines, especially if it's a cold reading. After you sign-in, relax, breathe deeply, and run your lines before the audition. Block out the actors, don't compare yourself, just focus on yourself and know that you will land the audition.
Walk into the audition room with confidence and a smile. Say, "Hello." Find your mark, which is usually a piece of tape on the floor, and stand there. State your name for the camera. Listen to the directions of the casting director. Give it your all, don't hold back. Listen to the other character and react accordingly. Thank the casting director and leave.