This is a question that has been asked/answered many a time on this forum. My first piece of guidance would be to search this site for previous questions/replies on this topic, there is a lot of good advice.
Next, what RCM services are you offering, and are they competitive with your targeted area for both services offered/pricing?
If I see a billing company that says they will only charge X%, and I know that the work involved means they should really be charging MORE than X%, I have to wonder about what kind of service I will actually be getting.
To somewhat parrot Richard, what experience do you have that puts you ABOVE other billers/billing companies?
Things I wouldn't continue doing: cold calls and emails. As a practice manager, there is nothing I hate more than cold calls for services, and emails for services. The cold calls are answered and told not to call again, and the emails go into the Trash folder. If I want a service for my office, I will research and call companies on my own.
Best advice: I have often found that getting your first client is all about who you know, and who that person knows. Word of mouth is the best way to get clients, many times. Every successful billing company I have ever worked for got their first client by knowing someone, and once they proved themselves, they went back to that client, and asked to be referred, and got more clients.
I am not saying this is the only way to get clients, but it is definitely one of the most successful ways.