Start a private studio to give yourself a solid student base and provide a steady income. Advertise in local newspapers, online search engines, grocery stores, malls and music stores. Make a list of all the places in which you can advertise and build toward a studio with at least 20 students.
Contact the local singers union and ask about registering as part of the union. Unions help singers and performers to find singing jobs, protect their rights as a singer and provide professional resources. Find a satellite office located in your state for a national singers union.
Place advertisements offering your singing services to composers and artists that need a professional vocalist for projects. Often, you can find listings for "singers wanted" just by visiting a local music store or the music department of a local university.
Audition for singing jobs that are listed through your local singers union and the National Association of Teachers of SInging. Join mailing lists and subscribe to professional singing organization newsletters to receive information about auditions and locations. You can find information on opera, musical and national groups looking for professional singers.
Sing for charity work and provide your services for free. While this may not be desirable at first, it provides an entrance to paying jobs which require that you demonstrate your competence in a live concert. Keep a list of all of your concerts. Think of each concert as a job and list it on your resume.