There are a lot of things you can do to help you sign that first client.
Look to volunteer at a doctor's office or a billing office
Take the 16 free courses offered by Medicare's Learning Network
Try to find old, unpaid claims to work on.
Volunteer in your community to help Seniors with their claim denials and appeals. You'll get good experience in dealing with Medicare.
Network with other billers by joining email groups, listservs and attending live conferences.
Join a reputable association (one that's been in business for a while)
Become a member of the BBB, SCORE, Rotary Club, your local chamber of commerce, etc.
Make your business card into a mini brochure that you can hand out anytime
Market to everyone you can
If you're having a hard time getting clients, you haven't got enough experience to sell a doctor or you aren't working hard enough at getting a client. That's the bottom line.
This job takes a lot of hard work and learning. Selling is hard work, too.
It's not one thing you do to get a doctor, but EVERYTHING you do. So do a lot and utilize promotional methods you like, such as cold calling, direct mail marketing, etc.