Customers connect everything they see to your restaurant. They don’t care that they are only walking through your parking lot, or on the street by your place, they will hold you responsible for anything they see that they judge to be messy or unacceptable.
I had a whirlwind three day stint at Jack-in-the-Box when I was a teen. After the third day, they fired me and told me I wasn’t made for fast food. Hell, I could have told them that. I must go back and thank them someday. On my second day, the manager asked (told) me to go out to the parking lot and drive-thru and scrape up all of the gum. I looked at her as if she were joking. She wasn’t.
At seventeen, I didn’t appreciate where she was coming from, now I do. If there is gum on the sidewalk by your place, scrape it up. If there are a bunch of cigarettte butts, pick them up. If it is the fall and there are leaves all over–rake them up. If it is snowing, shovel the snow. If a dog made a mess, pick it up. If there is a homeless person passed out on the sidewalk by your place, ask them to move along. All of those will be connected to your restaurant, fairly or not, by the customer heading into your establishment.
And while we are on the topic of outside your restaurant, don’t have your employees hanging out in front smoking and carrying on…designate a spot for that, and make it out of eyesight of the customer.
Remember, this whole restaurant thing is just a big show. Let your employees do all of that stuff backstage and keep the stage clear for the main event.