Follow whatever dress code is requested on the invitation or suggested by the host/hostess.
Arrive at least 10 minutes early unless otherwise specified. Never arrive late!
It is proper to bring a small hostess gift, one that the hostess is not obliged to use that very evening. Gifts such as flowers, candy, wine, or dessert, are not good hostess gifts, as the hostess will feel that it must put it out immediately. You must not never expect your gift to be served at the dinner party.
At a dinner party, wait for the host or hostess sits down before taking your seat. If the host/hostess asks you to sit, then do. At a very formal dinner party, if there are no name cards at the table, wait until the host indicates where you should sit. The seating will typically be man-woman-man-woman with the women seated to the right of the men.
A prayer or ‘blessing’ may be customary in some households. The dinner guests may join in or be respectfully silent. Most prayers are made by the host before the meal is eaten.
Sometimes a toast is offered instead of a prayer. Always join in with a toast. If the host stands up during the toast, also stand up.
Serving tea or coffee signifies that the formal part of the evening is over. Guests may now feel free to leave, or linger if the host or hostess encourages them to do so.
After a formal dinner party, a thank you note should be sent to the hostess.
Food is served from the left. Dishes are removed from the right.
Always say please when asking for something. At a restaurant, be sure to say thank you to your server and bus boy after they have removed any used items.
Butter, spreads, or dips should be transferred from the serving dish to your plate before spreading or eating.
Passing dishes or food:
Pass food from the left to the right. Do not stretch across the table, crossing other guests, to reach food or condiments.
If asked for the salt or pepper, pass both together, even if a table mate asks for only one of them. This is so dinner guests won’t have to search for orphaned shakers.
Set any passed item, whether it’s the salt and pepper shakers, a bread basket, or a butter plate, directly on the table instead of passing hand-to-hand.
Never intercept a pass. Snagging a roll out of the breadbasket or taking a shake of salt when it is en route to someone else is a no-no.
Always use serving utensils to serve yourself, not your personal silverware.
Do NOT talk with food in your mouth! This is very rude and distasteful to watch! Wait until you have swallowed the food in your mouth.
Always taste your food before seasoning it. Usually the hostess has gone to a lot of work making sure the food served is delicious to her standards. It is very rude to add salt and pepper before tasting the food.
Don’t blow on your food to cool it off. If it is too hot to eat, take the hint and wait until it cools.
Always scoop food, using the proper utensil, away from you.
Cut only enough food for the next mouthful (cut no more than two bites of food at a time). Eat in small bites and slowly.
Do eat a little of everything on your plate. If you do not like the food and feel unable to give a compliment, just keep silent. It is acceptable to leave some food on your plate if you are full and have eaten enough. If the food served is not to your liking, it is polite to at least attempt to eat a small amount of it. It is never acceptable to ask a person why they have not eaten all the food. Don’t make an issue if you don’t like something or can’t eat it - keep silence.
Even if you have dietary restrictions, it is inappropriate to request food other than that which is being served by the host at a private function. If you have serious dietary restrictions or allergies, let your host know in advance of the dinner.
Do not “play with” your food or utensils. Never wave or point silverware. Do not hold food on the fork or spoon while talking, nor wave your silverware in the air or point with it.
Try to pace your eating so that you don’t finish before others are halfway through. If you are a slow eater, try to speed up a bit on this occasion so you don’t hold everyone up. Never continue to eat long after others have stopped.
Once used, your utensils, including the handles, must not touch the table again. Always rest forks, knives, and spoons on the side of your plate or in the bowl.
Unfold your napkin and place it on your lap. When you are finished, place it loosely on the table, not on the plate and never on your chair.
Keep elbows off the table. Keep your left hand in your lap unless you are using it.
Do not talk with your mouth full. Chew with your mouth closed.
Guests should do their best to mingle and make light conversation with everyone. Do not talk excessively loud. Give others equal opportunities for conversation. Talk about cheerful, pleasant things at the table.
Don’t clean up spills with your own napkin and don’t touch items that have dropped on the floor. You can use your napkin to protect yourself from spills. Then, simply and politely ask your server to clean up and to bring you a replacement for the soiled napkin or dirty utensil.
Loud eating noises such as slurping and burping are very impolite. The number one sin of dinner table etiquette!
Do not blow your nose at the dinner table. Excuse yourself to visit the restroom. Wash your hands before returning to the dining room. If you cough, cover your mouth with your napkin to stop the spread of germs and muffle the noise. If your cough becomes unmanageable, excuse yourself to visit the restroom. Wash your hands before returning to the dining room.
Turn off your cell phone or switch it to silent or vibrate mode before sitting down to eat, and leave it in your pocket or purse. It is impolite to answer a phone during dinner. If you must make or take a call, excuse yourself from the table and step outside of the restaurant.
Do not use a toothpick or apply makeup at the table.
Say “Excuse me,” or “I’ll be right back,” before leaving the table. Do not say that you are going to the restroom.
Whenever a woman leaves the table or returns to sit, all men seated with her should stand up.
Do not push your dishes away from you or stack them for the waiter when you are finished. Leave plates and glasses where they are.
Never turn a wine glass upside down to decline wine. It is more polite to let the wine be poured and not draw attention. Otherwise, hold your hand over the wine glass to signal that you don’t want any wine.
Where a different wine is served with each course, it is quite acceptable to not finish each glass.
Source; United States Etiquette Guide