I completed research for a state agency that wanted to promote medical
billing as a viable home business for people living in small rural
communities. What the research revealed is that most hospitals and medical
clinics, primarily because of HIPPA regulations, are reluctant to hire
outsiders to do their medical billing. One primary reason is that the
hospital or clinic cannot control who may have access to the patient
information when it leaves their office. They don't know how secure your
computer may be or who in your office or home has access to your computer.
Patient identity theft is a big issue and the hospital or clinic is
ultimately responsible if it happens. Therefore, many hospitals and clinics
will only deal with former employees when choosing a medical billing company.

You may want to do research of your own to find out if HIPPA is a major issue
that might hinder your ability to obtain work. If so, then address how you
protect patient information in your marketing materials.

PPC For medical practices would be best on Direct marketing.

Hi Lisa,  Check our our Ultimate Guide to Small Business Marketing. It's a compilation of our best blog posts and guides that should provide some useful information, too.  

Direct marketing to medical practices would be best. Some paid per click
advertising and a nice website for those that do their research online would
be a close second.