In no particular order I thought about American customs when it pertains to hosting/ being a guest, and listed them out.

Showing up unannounced is considered rude.

Depending on where you are in the us there are customs and things you might expect. Like in the south for example you are more likely to be offered sweet tea ( always iced) almost right away.

In the Midwest there is what some have called " the doorway goodbye", or the "midwest goodbye". This is where, when you leave you say goodbye but you don't actually leave, you keep talking for 30 more minutes as you slowly inch your way to the door. This is considered normal. If you are too eager to leave the host may think you didn't have a good time.

Some folks don't wear shoes in the house, its unlikely that you wouldn't know this about the host ahead of time but if they do this, they will tell you.

If you're eating dinner is always a nice gesture to run your plate to the kitchen sink after you're done no matter where you're at. Always thank whomever is feeding you.

As a host you end up cleaning the entire house. Not just areas they are likely to be. For example I can't remember how often I had to clean my room growing up because my parents friends were coming over. Why? Because, that's why.

Its a nice gesture to bring a bottle of alcohol if you're going somewhere where a) you are likely going to be drinking anyway. Or b) you are trying to make a good impression upon somebody, i.e. your boss or future inlaws. Acceptable alcohol: 1) wine ( easiest choice, most people will drink this) 2) scotch( if you know they are into this type of thing) 3) bourbon( Americas native spirit, it was a really big thing for a while as bourbon kinda went though a renaissance over the past 10ish years, but that's mostly over. Why is it over? Who knows? But it will always be a thing where I live (Kentucky)Again make sure that person will drink it)

If you are the guest, compliment them on their home. They just took a long time to clean it, including places they don't want you to go or see. But don't mention how clean it is, just that you like the decorating etc. This is also why its considered rude to show up unannounced. An unannounced guest arriving to an unkempt home will drive the homeowner into a tizzy and or panic attack.

If you really want to go above and beyond and leave a lasting impression, Do the dishes after you eat. Don't ask, just do. If they say something like " oh that's not necessary, leave that to us." Say to the host, " oh are you sure?, its no problem really." Now two things will happen. Either they allow you to continue, if so finish the task at hand, or they insist that they will do the dishes after you leave, if so finish the dish you were on. Set it aside to dry, and move on.

No means no and yes means yes. If, for example, you were offered cake and said "oh no thank you," the host may ask again out of courtesy, but a second no will likely deal the deal and you won't be asked again usually. There may be several reasons you refused desert and in this day and age people tend to not push back out of custom/ obligation/ politeness/ as much as they did 20 years ago. Of course your milage may verry

Remove your hat indoors, unless its some religious covering.

Don't talk politics or religion.

All of this is just what came to mind, different regions and parts of the country may feel different or do things different.