Definitely study the phonology of the desired accent you'd like to master. Wikipedia is a great place to start. If you'd like to learn the Received Pronunciation (standardized British accent we non-British hear most often) you can start here: https://en.wikipedia.org/wiki/Received_Pronunciation Once you've mastered the individual sounds you can move onto intonation and style of speech by listening to lots of British TV, youtube videos, etc. Listening really helps the brain understand and help you speak the accent. When you're comfortable you should look into finding a language partner who speaks with the accent you want to emulate. Youtube also has lots of videos explaining pronunciation. Google is a learner's friend :)

A good place to start is vowel sounds. If you know which accent you would like to have, listen to someone, and listen to the way they pronounce their vowels. That will help you a lot. You also need to remember that your pronunciation needs to be pretty good before you can try to emulate another accent, otherwise the mixture of accents may make everything worse.

Yeah, sure. I mean the standard ones, like from the people who lives in london

me too

Which British accent? There are probably more accents in Britain than there are in the rest of the English speaking world!