Scientist have discovered that are brains are wired for sociability. We crave human interaction, we like being with people and where people are. The food actually tastes better and the experience is much more memorable if the restaurant is full. There is a certain amount of unease when you are eating in an establishment by yourself. Having the place full validates their decision to eat there. When the place is empty and the food and service appear to be good, there is a certain amount of cognitive dissonance that occurs, because there must be something you are not getting, otherwise you would not be dining alone.
People do not go to restaurants for food, they can get food anywhere. People go to restaurants to be with other people. Your objective as a proprietor is to create community in your place. Find innovated ways for your guests to interact with each other. Have them become a community and they will market your establishment for you.