Take acting classes. While this cannot be underestimated, it is essential. Although classes may take months--sometimes years--to complete, it's difficult to become a great actor without honing your craft. Many successful actors continually study their craft. You can be a working actor while still enrolled in classes, so make that your first step. Besides, it looks great on a beginner's resume.
Work on your "special skills." These are things that you can do that may give you an upper hand when being considered for an acting part. All actors must include a special skills section on their resume, and it can be anything. Sit down and make a list of all the hobbies you've had, sports you've done, types of dancing you know, accents you can do--any skill that can be of use to someone casting a part. Characters are as varied as human beings are, and you never know if that unusual skill is just the thing a casting director needs...and the thing nobody else listed on their resumes.
Work on your resume. Never lie on a resume, especially as an actress. Show business is a small industry in any city--even Los Angeles or New York--and you'll be surprised at how easily the facts stated can be verified or debunked. State your personal details, all past work experiences as an actress--even that little part in the school play if your resume is quite limited. State your educational history as it relates to acting. Also include something called "Special Skills" that you established in Step 2.
Get your head shot taken. Because you want to become an actress fast, it's best to work with a professional photographer. Let him know that digital is probably best based upon your time concerns, and inform him of your hurry. A photographer will let you know if he can give you a quick turn-around time. Many are willing to accommodate someone in a hurry. If you are in the Los Angeles area, Bjorn Photography is well-established as a head shot resource that delivers quality photography that can book you the job.
Submit your headshot and resume to anybody you can. When you are in a hurry, it's best to submit it to all the theater companies in town. Submit it to casting directors found in "Back Stage," a newspaper you should check weekly. Submit to every opening if you truly want to become an actress fast.
Submit your headshot and resume to the agencies listed in the "SAG" list. SAG, the Screen Actor's Guild, offers a complimentary list of franchised agencies across the country (see Resources below).