Some thoughts on basic etiquettes of entertainment, based on my experience as a diplomat.

Lunch (or luncheon), dinner reception and refreshments are called entertainment in diplomatic circles. Entertainment is important for socialising. They can be formal or informal.

If you are invited for a lunch or dinner, never show up empty-handed. It is usually considered inappropriate and, in some cultures, even disrespectful not to bring along a gift when invited for a lunch/dinner party.

The choice of gift depends on the occasion and the type of relationship with the host. Flowers are the safest choice. A decent cake or a box of chocolates is always appreciated. A good book (preferably fiction, a literary classic or a best-seller) is a great gift.

A fountain pen is also an elegant gift. A gift of pen or book shows that you are cultured. For male host, a decent gift can be a silk tie, a set of cuff-links or perfume. For a lady, a silk or cashmere shawl or a perfume works best. Avoid giving gifts that have no practical use.

If you are being entertained by the host at their home, always request them that you will bring the desert. Insist on it, politely, especially if you are coming along with your family. If you bring along a home-made desert, it will be considered very thoughtful.

It is advisable to eat light food before you go to a party, especially formal dinners. If you go to a party too hungry, chances are that you will not be able to observe the best of manners. You will not be able to concentrate on the host's conversation and will be busy eating.

Eating or drinking is never a priority at a party. Priority is your host and other guests (if any). It is important to enjoy the company, taste (not devour) food, engage in a good conversation and appreciate your host for making the arrangements.

Eat very small portions; pay attention to the dish suggested by the host. Don't forget to compliment the host for deliciousness of the food. There are multiple courses in formal dining, so be prepared beforehand for what to expect.

At the time of invitation, you can ask your host about the dress code and whether the dining will be formal. Choose a dress accordingly. Never be late, as it may ruin the planning and time management of the host. Never be early, the host may still be taking a shower.

If the party is indoors, it is considered polite to take off your shoes before entering the home (even if the host insists on not taking shoes off). Ask for hanging your coat (don't put your coat on a chair or sofa).

It isn't appropriate to use washroom while you are at someone's home. Although powder rooms (small WCs) are open for guests, avoid using them. You may just wash your hands. But visiting toilet & remaining absent for a while looks awkward. Do your dirty business at your home.

After the party, offer help in gathering dishes and taking them to kitchen. Never forget to tip household help (if she/he has been serving) and the cook (if the host is not the cook). Tips should preferably be in a plain envelope.

NEVER give money to child of the host. It is very impolite. You should be thoughtful enough to bring a book, a box of chocolates or a toy for the kid(s) of the host. If you didn't know that the host has kid(s), still you shouldn't give money. Kids aren't supposed to handle money.

Entertainment is a tit-for-tat business. If you have been invited once, it is then your turn to invite and become the host. You shouldn't be going to parties without hosting your own. If you and your spouse are terrible cooks, order food or throw a party at a good restaurant.

If you have too many kids, do not take all of them to a family party. If your kids are too wild & you've no nanny or other help, do not accept invitation (politely decline and state the reason). Kids are very predictable, they never fail to embarrass parents. This too shall pass.

If you are a guest, inform the host in advance about your diet restrictions (halal/vegetarian). If you are a host, make sure you know the guest's preferences and prepare food accordingly. It is essential to show respect towards people's culture and religion.

Don't speak too loudly during parties. Loud people look stupid. Take active part in conversation. Silence can be misinterpreted as something being off. Don't stay till late, look for cues of the host and take permission to leave. The poor host has to clean up after you leave.

Respect the host and their home. If the host has Persian carpets, they are not laid for the dirty shoes of guests. Try not to make a mess. If you are a smoker, don't smoke indoors. Never put cigarette's ash or butts in a glass, cup, saucer or a planter. Ask for ashtray.

Please refrain from touching decoration items in the host's home. There is nothing more embarrassing than breaking something at a party. Try not to get too excited at a dinner table; you may spill water or something else with your hands. Ensure presence of mind.

If your kid(s) are at the party, make sure they don't touch decoration or enter bedroom of the host. Kids love to jump on mattress and this may be the perfect opportunity for them to vent out their frustration. Be watchful. Don't allow their misbehaviour at any cost.

Have I been able to add something new to your information? If yes, I'll be glad to hear about it.
I'd especially love to hear from young students and professionals. They are our future.