British citizens do need to prepare before driving in the US, especially for an extended period of time. Any foreign driver needs to consider the legal requirements of driving in another country. In the US, it is especially important to compare car insurance options. A legal driver's license must be obtained to avoid any problems, and also to qualify for auto insurance. Legitimate car insurance companies do not cover illegal drivers. And of course, appropriate car coverage must also be obtained to meet legal requirements, and also to protect yourself from liability in case of accidents, damage, or theft. The best car insurance options, and driver's license choices, depend upon your situation.
According to usa.gov, which is published by the federal government of the United States, if you need to drive in the US, then be sure and obtain an international driver's license (IDP) before you leave your home country. In the UK, you can find applications at some post offices or from some automobile associations.
If you plan to stay in the USA for an extended period of time, you should plan on getting a license in the state you are living in. Driver's licenses are issued at the state level, but those licenses will allow you to drive legally in any one of the 50 states. Different states do have different residency requirements, so you will have to contact the bureau in your resident state for information. IDP licenses do expire after a year, and also, you will probably get the best auto insurance quotes with a valid US license.
Some British car insurance companies do cover foreign driving, but some also have a restriction of only covering foreign driving in EU countries. The US is not a European Union country. If you do not know if your current car insurance will cover you in the US, be sure and check before you drive. If you are not covered in the US with your current UK company, be sure and look for US auto insurance companies that will extend coverage to foreign visitors. Many of the top US car insurers do provide this service.
If you plan to depend upon rental car insurance, of the type that might be provided by a rental car company or your credit card, some caution is needed. Rental car insurance is designed to protect the rental car company first, and then to protect the consumer second. It may cover damage to the rented or leased vehicle, but not provide liability or injury coverage. There have been examples of US citizens who did not own a car, or keep their own auto insurance, incurring a significant liability because they were judged to be at fault in an auto accident when they rented a car and relied upon rental car insurance.
Every state in the USA requires proof of financial responsibility in order to drive legally. For most drivers that means they must meet the minimum liability insurance requirements. Make sure that the insurance you obtain will provide liability insurance. If you do have an accident, or if you are stopped for a minor traffic violation, proof of liability insurance will just make the event a minor inconvenience. The lack of liability insurance can get you in significant legal and financial trouble.