Word Of Mouth is the sole source of patients for most dentists in India. This means giving the best services to existing patients so that they refer more patients within their circle.
This 'word of mouth' acts as a chain of events that, given time, can lead to a good number of monthly new patients coming into the clinic.
The issue with only using the above strategy is, firstly - word of mouth takes a long time to develop, so you might need to wait a couple of years to make this strategy effective. Secondly, each business (a clinic is a business) should have multiple strategies to become profitable.