Pretty open ended question. My main advice: make sure you get a big raise between your UK salary and your US salary. In the US salaries are usually higher, but you'll have more expenses.
I'm originally from Europe (not the UK), and I like to say (even though it's not completely accurate) that most countries in Europe are "all-inclusive": high taxes/contributions, but you get good services for free (good schools, day care, health insurance, etc). The US is more "a la carte": lower taxes, but you have to be responsible and pay for the services that matter to you.