Perfect your reading voice. Practice reading out loud as often as possible. Work on your diction and word pronunciation. Speak clearly and pace yourself when you read. If you have even a hint of an accent, try not to use it. The ideal voice for audiobooks will not have any distracting elements. Your voice should take a backseat to the words you're reading, allowing listeners to focus on the story and not the delivery.
Join the Audio Publishers Association. It isn't necessary to join this association to work in the audiobook narration field, but the organization offers many networking possibilities. The Audio Publishers Association also maintains a listing of professional audiobook narrators that can be accessed by publishers seeking narrators.
Secure an agent. Voice-over agents specialize in finding work for narrators and voice-over artists. You can find listings for these agents online at no charge (see resources). Submit a sample of your voice, a query letter, and your resume to these agencies to secure agency representation.
Query publishing companies that specialize in audiobooks.