Despite speaking the same language, the culture is more different than one might expect. It is a separate country with just a few American things. They have their own brands, stores, and products you may have never heard of. The entertainment industry overlaps slightly, but the bulk of the television programming and music industry is British, most celebrities and sport stars you probablly had never heard of before.
The shops are not open the extended hours we're used to, except for a few if you’re lucky enough to live near one of them. Terminology is different, some spellings are different and so are some pronunciations. Basic everyday life has subtle differences and the attitudes are also different.
Some things you will have to relearn, so it helps to approach it as an adventure, that sometimes never seems to end. You'll need to relearn handling money. Imagine walking into a supermarket and not recognizing 90% of the brands, guessing which toilet roll, or cleaners are best. Recipes will be given in metric, weighing your flour on a scale in grams instead of levelling cups. The controls on the appliances will look foreign, you'll almost need to relearn to use a washing machine, a dishwasher, or the heating system with no thermostat.
See our forum Discussion of Pros and Cons, USA vs UK.