When British and American people invite you for a meal, it's useful to know these things.
Dinner parties usually start between 7 p.m. and 8 p.m. and end at about 11 p.m. Ask your hosts what time you should arrive. It's polite to bring flowers, chocolates or a bottle of wine as a gift. And you can say how much you like the room, or the pictures on the wall. But remember —it's not polite to ask how much things cost.
Usually dinners start with drinks and snacks, or probably start with soup or something small, and then you'll have meat or fish with vegetables, and the dessert, followed by coffee. It's polite to finish everything on your plate and to take more if you want.
Did you enjoy the dinner? Call your hosts the next day, or write them a short "thank you" letter. British and American people like to say "thank you, thank you, thank you" all the time.