Do...
Find out the meal times, and arrive on time and properly dressed: but not prematurely, or as the gong rings. This suggests that you are either greedy, or being starved, which is a rude comment on the commissariat.
Bring a guest-present. Drink is traditional: but awkward if it is a teetotal house (bad news), or already has a cellar that is grander than thy purse can buy.
Eat what you are given, without comment, other than praise for the hostess/cook.
Be thou familiar, but by no means vulgar. Give thy thoughts no tongue, nor any unproportioned thought his act.
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Don’t ...
Offer money for the groceries or insist loudly on buying rounds of drinks. This is a custom in some American host/guest relationships. But bad manners and ostentatious in the UK.
Take too much at meals, or leave too much on your plate. If there is something that you simply cannot stomach, hide it beneath mashed potato.
Bring your dog(s), cats, horse, hamsters unless directly invited to do so.
Bang on about the astonishing prowess of your darling daughter on the cello, or your son’s skill at Greek verse. Instead, show a warm interest in the achievements of the children of your host.