Keep the class, in middle class

Turn your cell phone OFF during dinner.

Don't slouch when talking to your company, keep eye contact.

Do not keep your company waiting because you're taking photos with your girls in the posh washroom!

Make reservations, do not show up at a restaurant expecting a seat. Learn to plan things, do not put your company through the burden of searching for another restaurant on foot. She might be wearing uncomfortable heels, or he might be injured.

Wear the appropriate attire, know the difference between a evening suit/jacket, and a day/working jacket. Vice-versa on the dress. Take the time to learn about clothing etiquette, understand your clothes. Don't have your company thinking you made no effort, and they are just someone you needed to book a table at a restaurant in your after-work clothes.

Men get the fucking bill.
Ladies if you owe the guy, make an excuse to go to the washroom and get the bill without his knowledge. Most Men's ego will not allow for a woman to get the bill. Don't be cheap.

Don't talk about your ex, never fucking mention your ex. Date or casual dinner, fucking annoying.

If one party doesn't smoke, don't go for a bloody smoke during dinner!

Don't ask the waiter of his sexual orientation just because you're curious, especially if the waiter went to school with your company. Poor bloke.

Compromise. Don't order the wine you want, order the wine that is good for both you and your company. Some girls can't take the richness of Bordeaux, you're aim is not to get drunk.
Girls, don't act cute or obnoxious just because you want to get your way. Nobody wants to drink with a bitch.

If your friend is treating you to dinner and it's not over someone enormously special, don't order the fucking lobster & caviar.

Don't offer to taste the wine if you don't know what the bloody hell you're tasting for.

Don't mess with the people who handle your food, just because you want boogers and sneezing in your food, doesn't mean your company does.

DON'T TAKE FUCKING PHOTOGRAPHS OF YOUR FOOD! WTF IS WHAT THIS RIDICULOUS OBSESSION?! Do you work for the restaurant? Restaurants critics don't do it, why the bloody fuck would you?!?!?!

Ask before taking food off of your company's plate, some people very much dislike sharing food in particular.

If you dig your teeth into all of your company's starters, pay your share.

Don't order anything that will render yourself incapable of participating in the activities you have planed with your company afterward. Be adventurous, don't be stupid. There are less obvious ways to ditch someone.

If you don't feel like eating, order a drink. Never leave your company eating alone, very very rude.

Offer the seat with the better view to your company.

Finally, pull the seat out for the lady if you're a guy.