1. Improve your curb appeal. Is your sign fully lit? Did someone empty their car's ashtray in your parking lot? Are the flowers in the planters alive? Is your sign fully lit? Before a guest even enters your building they have started to get a first impression about what to expect. If it's bad enough, they might just get back in to their car and leave.
2. Clean your restrooms. The restroom lets you know what a restaurant's cleanliness habits are. If the bathroom isn't clean what does the kitchen look like? While you're at it, fill the soap and paper towel dispensers, and get rid of the nasty smell. Nothing ruins my appetite like a poorly-kept restroom.
3. Clean, clean, clean. I'm not just talking about the basics such as cleaning your bathrooms, vacuuming the floor, or cleaning the windows. I'm talking about cleaning the bottom of the sugar caddies, and making sure the squeeze bottles of ketchup and mustard don't have dried gunk on them. The edges of the tabletops, and the bottom side where someone has deposited their chewing gum should also get some love. And, when is the last time the seats in the booths were removed and cleaned?
4. Hire good people and train them. Your staff represents you, and sometimes they might not represent you well. Individuals who don't perform quality work should be held accountable. Everyone needs training on the menu and menu item ingredients, how to address a table, and how to respond to a complaint or concern. When someone tells your staff that they are a first-time diner, your staff know how important it is to make a good impression. And when asked for their opinion as to "what's good", the answer shouldn't be "everything".
5. Touch tables. It seems to be a lost art unless I'm paying $40+ for an entree. Why don't managers take the time to touch tables and inquire as to how the dining experience is going? The cost of this seemingly rare practice is nothing, and the impact can be great! Just because a restaurant is "casual" doesn't mean that the manager or chef shouldn't be able to say "hello". And once they do touch a table, they need to respond appropriately to a guest's complaint and make things right instead of making excuses.
If any of these issues applies to your restaurant, you need to stop what you're doing and take action NOW. You'll be surprised at how just improving on the points above will improve your restaurant's image, and improve your business overall.