1. People like their food better.
Is it the portions, the flavor, the price, or all of the above? Do they have a signature item people crave?
SUGGESTION: Experiment with new items like sweet potato fries. Give a complimentary serving to every customer for 2 weeks and closely track how many of them eat the whole helping versus how many leave it largely uneaten. Add the winners to the menu and put a big sign outside (or in the window) announcing the new menu item. "Try our Sweet Potato Fries!" Dollar for dollar, it's the best advertising you'll ever do.
2. Their service is quicker.
Very few people will tell you that your food is boring, your portions are small, or that your service is undependable. They'll just smile and tell you everything was fine. Then they'll leave and not come back.
SUGGESTION: Put something to eat in front of the customer immediately. Interesting pickles, chips, crackers, bread, whatever. Move quickly. Shorten the time customers have to wait to place their orders. Never make a customer wait for a drink refill or their check.
3. They deliver a more comfortable environment.
A broken sign outside, faded drapes in the windows, dusty mini-blinds, wobbly tables, dirty air vents or ancient notices on the bulletin board give a place the feel of death. Look at your eatery through the eyes of your customer.
SUGGESTION: Spend some real money on your bathroom. What your customer sees in your bathroom is what they imagine in your kitchen. Keeping a public bathroom sparkling is relentless, hard work, but you're going to be surprised how much it impacts your customer count.
The food service business is hard because customers have high expectations. I wish you well.