These days if you run a restaurant, you need to have social media.
In my opinion, the best options would be Facebook and Instagram. Along with this, if a website for the restaurant is created, it builds the brand and image of the restaurant. Get articles from food critics, blogs etc. posted on this website helps with the engagement of guests.
If you open a restaurant, it is a good option to provide free WiFi for guests dining at the restaurant. When you offer this service, ensure the guests log in via your Facebook page and become a friend of your page.
Why is this important? It is essential simply because they are more likely to post on his Facebook on his dining experience at your outlet. This will reach his friends who can also check your restaurant out as you are a friend of this guest. Its a simple mechanism of friends introducing friends. In the process, you grow your network and bring greater awareness for your restaurant and what you serve.
Facebook gives you options for marketing - simple boost mechanics that help reach target diners in the vicinity. Costs are minimal and something you can control - you do not have to do any newspaper adverts. Facebook also enables you to interact with diners by answering their questions, requests etc. which is why having Facebook, but not having someone respond to this, is ineffective.
Your content on Facebook should mean the diners want to come and try your food simply from the picture they saw or from a great experience from one customer. If there was a bad review, you have to explain what happened to ensure there are two sides to the story of the diner. If you are wrong - admit, apologise and ensure you invite the guests to come back and see the chef personally for a chance to deliver a second chance.
In the case of Instagram, you post pictures with simple tag lines. You arouse the interest of the viewer by seeing the picture. It helps boost the reach of the audience, but it is less interactive than Facebook in my opinion.
Whatever tools you use, ensure it is done with a clear objective what you wish to achieve and followed through in detail and respect the privacy of each user.