When you are in a public place, pay attention to your surroundings. Sit or stand in a position that makes it easy to do.
My wife is so used to my routine when we go out to eat that she knows where to seat herself and the children without even asking me. She knows I'll ask for booth instead of a mid-floor table, and she knows I want my back to a wall with the entrance in view.
The strategy comes from many years of carrying a firearm concealed and from being a private investigator. I prefer booths because I will not accidentally "print," which means one of my firearms shows through my clothing. A booth also means no one will accidentally bump into it. Plus, a weapon could be accidentally exposed, and no one around me would easily see it.
You do not want to be the man on the right and have your back to the entrance. He's not paying attention at all actually, and a person with a firearm could walk in without him even seeing them. His situational awareness, the ability for him to pay attention to everything around him, is very low.
You may think following this advice is paranoid, but I have colleagues and friends who do even more. They will case the establishment in advance and take note of all the entrances and exits. In addition to sitting with their back to a wall with the entrance in view, they will also be next to a secondary exit. This strategy can be very involved and taken even further if desired.
For me at least that is too much trouble, and I settle for saying, "booth please" to the hostess. Then I do my best with the seats they offer. Asking for much more would bring a lot of unwanted attention to my family. If I was there for a meeting with a client however, I would take extra precautions.
Speaking of taking precautions, I would like to share a common private investigation case.
Unfortunately, there is a lot of infidelity in the world. Private investigators are often hired to test for and document it too. Some people think being flirtatious when their significant others are not there is acceptable. But if you are married, you have agreed to a contract. You agreed to be faithful.
It isn't just for married couples either. If the other person expects you to be faithful, you should be. Some people have "open relationships," and that's fine. If you're not in one though, keep your word. Be faithful. For those that cheat, remember private investigators are regularly hired to catch you.
They do it through regular surveillance, but sometimes things are taken a step further. It is a gray area that some private investigators disagree with, but decoys will be used. A decoy is a person who will purposefully go up to the subject and flirt with them. Then the investigator gets the person's response on video.
Some people may think this is entrapment, but I have seen pretty damning cases. In one example a man thought his fiancee was cheating, so he hired a firm that used decoys to test the loyalty of his future wife. The decoy walked up, introduced himself, and asked if she was single. She said yes and ended up hooking up with the guy.
People hate it when other people give unsolicited advice, but I'm going to do it anyway.
If you are lying, you will eventually be found out as a lair. If you are cheating, you will eventually be found out as a cheater. No one gets away with unethical behavior forever. My advice to you therefore is to be ethical. Don't lie to people, and don't cheat on them either. Oh, also do as you say you'll do, and don't try to defraud people!
Recently, I had a person, who I thought was a friend, lie to me. She was caught in a couple small lies at first, and then I found out about a huge one. She was planning on stealing from my friends, and I had a moral responsibility to protect them. I'll never understand why such people think they'll keep getting away with their schemes.
My spouse had my back and fought publicly, causing a lot of drama, to expose the truth. Without her actions though, I may have taken longer to discover it. She helped to "break the case" far more quickly. She also prevented a huge fraud from occurring. Thanks, 
