Be sure to tell them their life would've been much better today if they remained a colony

They're driving on the right side.

Good luck not getting shot mate.

Bring a printed copy of your ESTA / visa for immigration. Get some kind of travel insurance that covers health emergencies, and have proof of that printed as well.

My condolences

Americans

Hello fellow Brit.

Everything is bigger. That's an obvious statement, but the knock on effect is that nobody seems to have a sense of "nearby". I frequently went out running on the pavement around two or three blocks, and people either looked at me as if I was possessed, or honked their horns like a "run Forrest run!" type thing because there was literally nobody else out putting miles on tarmac.

Retail parks are a cracking example. I was out with a friend who knew the area well, and we wanted to go from one store at one end of the retail park to the other. I was happy to walk the three or four hundred metres and back, but they were positively horrified at the thought of not taking the car to another parking spot there.

Speaking of driving - know your rules. Four way intersections are a cool invention. ~~Roundabouts~~ traffic circles are fucking wild going in from the right.

See those 300, 200, 100yd marker boards on A-roads and motorways allowing you to figure out what lane you need to be in to take your slip road? Purely optional in the US. Be ready for people in lane three (or four, or five, or six) to see their exit and cut straight across. Blind spot checking is for nerds and communists.

Things have changed lately, but go out with two or three changes of clothes, and that's it. The clothes in the US are generally much cooler and much cheaper, it's a good excuse to get new gear. Depending on where you're going though, it's hard work getting particular stuff - asking for Under Armour's heatgear stuff if you go running in winter will get you some real fuckin' weird looks in Florida, where even the vests are sometimes hotter than a duffle coat.

The border: know your shit - where you're going, how much you got, who you're with. The border force agents (whatever their unit is called) are generally super cool, but they ask super intrusive questions. That Marks and Spencer ham baguette you got in Gatwick/Edinburgh/Manchester? Eat it quick, because it isn't going through customs.

Not sure how long you're going for, but get a Post Office multi-currency card, or a credit card that specialises in the US Dollar or low international currency fees. While you're at it, feel free to wow them with contactless payments. Last time I went to CVS, I had tapped the card before the cashier had finished his spiel about swiping the card, and refused to believe I'd actually paid for a few seconds. It's like a magic trick with none of the effort.

Overt generosity is mostly viewed suspiciously. I left the DC metro system at a gate, and tried to hand off my all-day travel card for someone else to use for the day, and was looked at like I'd shit on their station concourse and drew a Greek flag in it. It's not like the tube.

Tylenol: get shitloads. It's basically paracetemol wrapped in bubblegum. Outstanding for hangovers.

Enjoy it! The Americans are friendly enough even if the majority of them make some pretty wack political choices, but that's another discussion. They're generally sound as fuck, and find the British accent something of a novelty, so feel free to use it as a get out of jail card if you make a social faux pas. (edit: I don't mean literally, I haven't tried it on police officers)

Have fun, let us know how you get on!

If you want to avoid getting shot, you should now wear a red hat, not a red coat.

Don't try to bring food. I've seen people stopped for smuggling meat. You're probably okay with packaged sweets or chocolate, but you should declare it.

Don't be fooled into thinking you can get tea if you see it offered. It may be some strange flavour, or very weak, or iced, or all three. And it will be hard to explain that you want milk and sugar with it.

Biscuits are good enough, but chocolate is rough.

And, of course, a "biscuit" will mean a type of savory scone.

If your shop, at most stores they will pack shopping bags for you and are a little shocked and overly grateful if you do it yourself.

Be prepared to tip in many circumstances (but not, oddly enough, for having your groceries packed).

Be prepared to be asked about football, the Beatles, the Queen, maybe even the King.

Don't be offended is someone attempts to do a British accent at you, it's meant as a friendly greeting.

If driving:

Four-way stops are like roundabouts without the roundabout. But with stop signs.

Pedestrians are not expected to look out for traffic, but are not allowed to just cross anywhere. So it balances out.

Someone has stolen the clutch pedals from all the cars.

Where in the USA are you going. Saying you're going to the USA is like saying you're going to europe. There's a vast difference between the different states and regions within those states.

Bring your own marmite.

USA is really quite safe, just remember to not be black or a woman

Oh and wear a ballistics vest if you're going anywhere near a school