These social rules mainly apply to the US but there may be some overlap in other parts of the West:
Always make eye contact in conversation. Put away the phone, book, laptop, or anything that can distract you from what someone is saying.
Don’t stay too long after a party is over. There is nothing more annoying than someone loitering in your house/room/apartment after everyone else has left.
Unless the host says otherwise, always bring your own food and/or alcohol to a party. Don’t take away the leftovers either.
“How are you?” is more of a polite greeting than an actual question if its coming from a stranger.
In an academic setting (especially in class or in a library), make sure the volume on your phone or laptop is off or set to vibrate.
As a general rule, save for some parts of the South, open racism and racist jokes are pretty taboo. We like to keep our racism implicit and systemic nowadays.
When you make eye contact with someone in public, nod your head up if its someone you know (or say hi) and nod your head down if its a stranger.
If its a stranger, avoid making eye contact for more than a second.
While standing, maintain a distance of at least 1 feet (30cm) from someone unless they are a consensual romantic/sexual interest.
Do not scratch or handle any of your private parts in public.
Z
When shaking hands, make sure you are standing up and making eye contact.
Don’t interrupt when someone is talking.
Don’t ask a woman whether she is pregnant or not.
Don’t ask someone about their weight or diet unless they bring it up and ask for your opinion.
If you borrow something from someone, make sure it is returned in the same condition it was in when you took it.
Always hold the door open for people that are behind you.
Always thank someone when they hold a door open for you.
Unless the service is exceptionally bad, you should tip at least 15% (preferably 20%) when eating out.
If someone offers up the last piece of food, it means they want it and you should refuse.
When entering someone’s home, ask if they allow shoes in the house.
If someone is paying for your meal at a restaurant, don’t order one of the most expensive dishes on the menu.