New regulations for travel to the USA have recently been introduced, and all British visitors need to ensure that they have a modern machine-readable passport issued in the UK. Britain is part of the US visa waiver program, and so you do not need a visa to travel to the country for a stay of up to 90 days - provided that you do not intend to work during your stay.
On entry to the USA you are required to fill in a form declaring your status as a British citizen, known as I-94, and these must be filled in for all passengers including children. Usually, the staff on the plane will pass these forms around prior to landing.
There are British Consular offices in many US cities including most major tourist destinations such as New York, Orlando and Los Angeles. Should you require assistance elsewhere in the country, you should get in touch with the main Embassy in Washington DC, and they will be able to advise you of your nearest contact.
British Embassy
3100 Massachusetts Avenue NW
Washington DC
20008
Telephone: (1) (202) 588 7800