Large brands started small, as they grew they send more and more communication to their potential market and became wold known.
Your 3-miles radius from your establishment is your zone of influence. They receive your postcards with your offer, if they see it so many times they eventually will come. Repetition is the new word-of-mouth in our electronic age. When they come, its up to you to keep them coming back with your Great Food at a fair price, Stellar Service and an Atmosphere where they feel Welcomed.
Constantly work on those three ingredients, and add communication to become the number one restaurant of your community.