The simple answer is that there is not as much difference as you would think.
Here's a situation. Imagine listening to a discussion between two business experts, one from London and one from New York, or two academics, one from Oxford and one from Harvard. There will actually be very little difference in the way that the two people speak. The GA speaker will pronounce the 'r' sound at the ends of words such as 'far' while the RP speaker will probably not. There will be certain differences in the way that some vowels are pronounced, particularly 'o' and 'a', and slightly different realisations of 't' and 'd', for example. There may be occasional stress pattern differences in one or two words. And that's about it. Otherwise, the two people will speak in a remarkably similar way. And I can guarantee that the average Chinese person would not be able to tell you which person was American and which was British.
In fact, there are more differences WITHIN English-speaking countries than between them. A Texas farmer will sound very, very different from New York taxi driver. Likewise, if were to record working-class British people talking in pubs in London, Liverpool and Glasgow, they would sound so different from each other that you would not believe that these people were even speaking the same language.
Obviously, in your case, you would not want to model your pronunciation on either the Texas farmer or the Liverpool dock-worker! Your aim would be for a neutral, standard, educated accent, and it really doesn't matter whether you model yourself on the Harvard academic or the Oxford one - the differences are minimal. And, needless to say, both are equally acceptable wherever you are in the world.