The more you listen to them, the better. Remember, it takes time and speak like them is not so easy. Try to sing some british songs and watch a lot of interviews.

Not only is it useful to try to watch and listen only to British programmes and songs, but I think that it is almost as important to avoid all American productions. This will help to tune your ear to the British accent and not be hearing the same words with a different pronunciation. As others have pointed out there are many British accents, probably the most useful to emulate would be known as 'The Queens English' or 'BBC'. Some regional accents aren't always understood by native speakers from different areas, but pick what you like the sound of to keep your motivation.

You can do what's called "shadowing". Basically, find the accent you like, and then listen to the same text over and over again. Hopefully, you have a transcript of what they've said or can hear well enough to create one. Then just practice shadowing that accent (maybe even try recording your voice at the same time) until there's no difference. There are also many teachers (such as myself) who specialise in accent reduction and modification. You could have someone help you specifically on those areas. I will say a few things worth considering: 1. Do you have a good ear for music? Are you good at imitating accents in your own language? If so, you'll probably be good at mimicking English accents given enough time and ear training. However, if you can't adapt to different accents in your own language, then it will probably be hard for you to do so in a non-native language. 2. What type of British accent would you like? The UK has a lot of different accents separated mostly by region but sometimes also by class/education level. If I were you, I would find an YouTuber (for example) with an accent you like, and then learn and follow their videos to work on their accent.

To my mind the best thing to do is listening to the way they speak in british accent then trying to copy it in your mind . One thing that truely helped me to have a better british accent than before was talking in my mind . Yea i know it sounds stupid but it really worked for me