Americanisms are a rich part of the evolving language, but older readers may not be so keen to be up to the minute. I have listed some words and phrases which are perceived as recent imports and are sometimes disliked, and the UK version (if there is one).
24/7: round the clock, or all day every day. Both are much longer than the snappy Americanism.
backyard, back yard: back garden
bangs, as in hairstyle: fringe
bathroom/rest room: lavatory
burglarise/burglarize (US spelling): burgle. I can’t see much advantage in using the longer American word.
chips in America means crisps in Britain. When they want to order fish and chips, they ask for fries.
closet: wardrobe. Obviously you can't change ‘he/she came out of the closet’ to ‘he/she came out of the wardrobe’.
closure: a lot of people dislike this word, but it does have a meaning of its own. The nearest alternative might be ‘peace’.
do the math: I don’t think you can reinterpret this as ‘do the maths’. Either use the US version or something else.
eatery or eaterie: dining establishment. I think this has an all-encompassing meaning which makes it useful.
faze: a most useful word, especially when you consider that the nearest alternatives are probably ‘discomfit’ or ‘discombobulate’.
garbage/trash: Usually rubbish in Britain
get-go: starting point
gotten: got. Certainly ‘gotten’ is pretty bad, but ‘got’ is not much better.
heads up: warning or advance information
hike: rise or increase. To hike, as in to walk or ramble, is not American as far as I know.
homicide: Americans use this instead of murder. In fact homicide is a term embracing all types of killing of one person by another, either intentionally or not, in line with other ‘cides’ such as infanticide and suicide.
hospitalise/hospitalize (US spelling): admitted or taken to hospital.
left field: it’s hard to find an exact equivalent. Maybe ‘unexpected’or ‘unorthodox’.
license: the US spelling of the noun licence, which you will see every time you switch on your computer.
normalcy: normality. Some authorities believe there is a subtle difference in meaning but I think it is too subtle to bother about.
outage: power cut
pled as the past tense of ‘plead’. In this country the form is ‘he pleaded guilty’, not ‘he pled guilty’.
raised (in a child-rearing context): brought up. I think this one is particularly unpopular.
reach out, touch base: make contact
shined: This is not a recognised UK past tense of shine. If the context is 'he shined his torch', the UK English word would be 'shone'; if it is 'his shoes were shined', we would say 'his shoes were polished/highly polished'.
specialty: I don't think the fact that it is one letter shorter is a good reason to use specialty rather than speciality.
truck/trucker: lorry/lorry driver
waiting on: usually ‘waiting for’. For example an American might say ‘I was waiting on the train’ which in Britain would suggest he was on board the train, not on the platform.
witness stand: witness box. I can see no reason to use the American version in a British context. Note that a person enters the witness box, he does not ‘take’ it.
These are American words and expressions which have no UK equivalent.
Black Friday: The Friday following Thanksgiving Day in the United States (the fourth Thursday of November), when major retailers offer promotions to mark the start of the Christmas shopping season. It emerged in the US early this century and really took off in this country in 2013.
prom (as in school dance or party)
trick or treat
Watch out for
curb is the US spelling of the British kerb.
story is a floor of a US building; the UK spelling is storey. Thus the US plural is stories, while the British is storeys.
sulfur is the US spelling of sulphur.