The difference one day makes
Contact the patient when the bill is one day past due. Set up a system that flags a patient's account when payment becomes overdue by one day. Give a staff member responsibility for contacting patients by phone -- calling their cellphone numbers if possible -- to politely but firmly remind them that they owe the practice money.
Don't delay ... but don't apply pressure. Script the one-day call so the patient perceives it as a helpful reminder. The mere fact that the practice calls within one day sends a clear message that you are on top of receivables -- and that yours is one bill that should always be paid on time.