For all their wealth and influence, there's probably no nation more misunderstood by the British than the Americans. This is mostly because of the pervasiveness of American films, music and television in the UK -- but even though this means it's really their fault, it's still a good idea to dispel a few of the most common myths about life in the USA.
You can get there from here
Everybody knows that America is huge. What they often don't seem to get is that it's ... huge. British travellers in the US have a bad tendency to think they'll spend a day at Disney World, pop up to New York for the weekend, and then swing by the Grand Canyon before heading home. It doesn't work like that. The best way to overcome this is to think of the US as several different countries, more like Europe than like France.
American television is responsible for a lot of stereotypes about the US: high schools where letter-jacketed jocks are treated like kings, tough big-city cops who don't care about the regulations, and quirky yet surprisingly clean neighbourhoods where cheerful young people trade witticisms. America has things that resemble these, but compared to the Hollywood version, the real thing is usually weird, complicated and somehow unsatisfying. Americans often tend to unconsciously assume that the TV version of life is real as well, leading them to be subtly dissatisfied with reality.
Everyone has a gun
The idea of most people owing a firearm is a bit strange to Brits, and can lead to nervous reactions. It's true that there are a lot of guns in America: in 2007 there were nearly 9 for every 10 Americans. But guns aren't spread evenly across the country -- some people, particularly in rural areas, own lots, while in many parts of the country gun owners are few and far between.
The crazy is everywhere
Every week, it seems like there's another story in the news about some high-profile act of madness in the US, whether it's the formation of some strange new cult, an apparently respectable politician spouting a ridiculous conspiracy theory, or a crackpot view being believed as if it were scientific fact. Partly this is just a function of how large the US is and how publicised its strangeness is. It can be a pretty weird place -- but then so can Britain. It's just that American lunacy is more in the spotlight.
No sense of irony
One of the most common notions about Americans is that they lack a sense of irony. This is based on two true things: first, the default attitude in American conversation is sincerity in a way that just isn't true in the UK. Secondly, American comedy often works by exaggeration, whereas British comedy is often more understated. But none of this means that Americans don't understand irony (The Onion or Futurama will suggest otherwise). It just isn't their normal means of communication.
Like big children
The perceived lack of irony ties in to another common misconception about Americans -- that there's something naive and childlike about them. This isn't so much a myth as a misinterpretation. It's true that the typical American is more open and sincere than the typical Brit, who tends to be more guarded and cynical. But that doesn't make them childlike, and it certainly doesn't make them stupid. If anything, it's a more mature approach than constant ironic distancing.
The beer is terrible
This stereotype isn't so much incorrect as it is outdated. Most American beer (like most British beer, let's be honest) is pretty dire, and perhaps it was once all terrible. Today, however, American breweries are catering to a more mature beer lover. Beers influenced by American craft brewing are even starting to make an appearance in British pubs. British beer snobs should abandon the stereotype of all Americans as Coors-swilling louts unless they're willing to accept lovely fizzy flavourless lager as the UK's national drink.
Made of money
The US is one of the wealthiest countries in the world, with an annual median household income over 25% higher than the UK's. But America being a rich nation doesn't mean that all Americans are rich. In fact, severe poverty is a fact of life for many Americans, and the conditions a typical Brit complains about would seem luxurious to some US families.
One landscape per state
When you say "California," most Brits think of palm trees and sandy beaches, which may describe Malibu or Santa Monica, but doesn't describe foggy San Francisco or the wooded hills of the northern part of the state. Similarly, British visitors who expect dusty Western landscapes might find parts of Texas surprisingly green.
No sense of history
"To a Brit, a hundred miles is a long way; to an American, a hundred years is a long time." It might be true, but the fact that the US@s history is short compared to Britain's doesn't mean that Americans are out of touch with their history or live in a perpetual now. Consider the use of Revolutionary War imagery by the Tea Party moment: it's hard to think of a historical image that would be as easily recognisable -- and so heavy with meaning -- for a British audience.
It's not the Queen's English
American English, with its strange pronunciations and stranger vocabulary, can lead Brits to think of it as some kind of deviation from British English. In fact, American English preserves a number of features of earlier British English; in some ways, it's closer to historic English as spoken in England than modern British English is.
The British stereotype of Americans as overweight has a lot of basis in fact: the US has one of the world's highest rates of obesity, with over 30% of adults being obese in 2008. But if Americans tend to be obese, they aren't much worse than Brits -- 23% of British adults are obese, according to the World Health Organisation. The differences shouldn't really be all that noticeable.
No public transport
Everyone knows that there's no public transport in America -- or at least no good public transport. At a guess, the "everyone" who knows this probably lives in Zone 1, because outside of high-density areas, American public transport isn't that much worse than its British counterpart, although like everything in the US it varies greatly from place to place. There are some great things about American public transit -- the fascinating views you'll see on a long-distance train journey, for instance.