I work with 3 Irish, 2 Scottish, 1 Welsh, and loads of English people. Having lived in Manchester, Nottingham, Leicester, London, working in Hertfordshire, and meeting people from Everywhere, I'm getting to the point where I can pinpoint people's regional backgrounds-- For me, it's a lot like what dels said about fine-tuning your ears to different dialects. But it's definitely an ongoing process!!
Talking about Burns Night/Haggis the other day, the word "Poem" was translated down the table from Glaswegian Scottish --> Northwestern Irish --> whatever version of American I currently speak, so that I could understand. I had NO idea what the Glaswegian had said and normally joke with her that I only catch about every 5th word that comes out of her mouth. Previously, I literally made her spell the word "Girl" because I thought she was saying "Ghetto". So personally, when I don't understand, I simply ask! (But mostly, I just stare blankly until we laugh about it together later).
My tips? Don't worry about it! I think your ears will naturally adapt to the funny nuances of British speech patterns, so what seems strange now, might sound normal to you later. Do you know where you'll be moving? I find the Posh Southeastern and London accents to be the easiest to interpret. Good luck!