This is kinda vague. What are your circumstances? Are you joining a school? University? The work force? The advice will be different for each. Also from your use of "y'all" I'm assuming that you're American so tailoring my advice to that, sorry if you're not lol.
School: Be aware of how different British schooling is to what you're used to. In most schools, you have 11 year olds in the same enviroment as 18 year olds. If there isn't a sixth form attached, it'll be up to 16 year olds. Depending on your age, this could seem really intimidating as an outsider. Education here is also extremely fast past and focused on deciding future career paths incredibly early on (I have noticed from American presence online that British teenagers in general are a lot more mature, and I think that this is why!), which again, could be seen as very intimidating if it's not something you're used to. You will find yourself cutting out subjects after only studying them for two years (at 13 years old!!), adding new ones in, preparing for mocks and assessments very early on. Try not to let any of this faze you, as if you're unprepared for it you'll look like even more of an outsider, inhibiting the friendship making process. Just take it all in your side and friendships will come naturally, as they do in school.
University: If you're staying in halls, leave your door open so people can walk past and say hi. Try and join as many societies as you possibly can to meet people with similar interests. Talk to people on your course that you see in lectures or seminars. Remember that everyone's in the same boat at uni, no one knows eachother so they're trying to figure it out as much as you are!
Work: This is probably the trickiest one tbh, as most people have their friendship groups established by this point. Just be pleasant and go out to drinks with people when invited to, and you'll get to meet people through friends and friends of friends.
General advice: You will be bantered A LOT whatever age you are about being an immigrant, being American, and having an accent. It's what we Brits do, I'm afraid. Although at times it may feel nasty or like it's getting too much, try not to take it to heart, there is 100% no malice behind it. Laugh along with it or respond with your own gentle banter back, as getting upset about it will both cause offense and make people think you're too soft: people don't tend to take kindly over here to when others respond to banter too seriously. Doing that won't win you any favours, trust me. Also don't try too hard if that makes sense? Be pleasant, kind, and approachable, but not too in your face with it. That is NOT the British way, and people will be affronted and almost slightly wary of you from the get go. A smile and a hello is fine, a full blown conversation with someone the first time you meet them is weird.