I'm a big believer in observation and imitation as a means of learning. In fact, it's what we tend to do as children - we watch the world and the people around us and try out their behaviour, their language, the way they use their body, and through this exposure and imitation we learn new things. And the more we practice them the more habitual and deeply ingrained they become.
These observation and mimicry skills never leave us (although in some they are not quite so well preserved), and it is through those same skills (and others) that we learn new things. So, if you're trying to learn a new accent, you absolutely need to surround yourself with those people who embody what you have the capable of doing.
Now you might be thinking, 'but how can I tell if they are speaking with a standard British English accent?', or 'but I don't know anyone who speaks in the accent!'. So you might start by searching google or YouTube for 'RP accent' or 'standard British English accent', or even ask a native friend if they can point out other people that you work with or socialise with who speaks in this accent and if they aren't any, ask them if they know of any one in the media (public speakers, politicians, news readers or actors) who speak in this way. You might find some podcasts, interviews or audio books featuring one of these people. For instance the politician Theresa May or actor Stephen Fry are good examples of people of speak in this accent.
Either way, whether they are real or in the media, listening and listening and listening to them, and observing and observing and observing them will help you enormously in your pursuit of speaking with ease like a native speaker. Surround yourself with the sounds and intonation of the accent, submerse yourself in the world and culture of the accent and you'll surprised at the impact that this submersible behaviour has on your learning. - which is, of course, what we did as children.
Essentially it gives you a model, something to base yourself on, to compare yourself to and to use as a source for exploring the accent.
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