Performance Theatre Resources

 
This is one of many excellent online videos for teaching British RP.  This guy is funny and his videos clearly show which sounds should be changed in order to begin your study of the British RP accent.  He has several videos, but I feel this one is the best to start your studies:

 https://www.youtube.com/watch?v=IIGAL77OuM0 

Here is an excellent clip from Sense and Sensibility that has a very good example of British Received Pronunciation:  

 https://www.youtube.com/watch?v=IIGAL77OuM0 

The character, Hermione Granger, also has a very good British RP accent.  You can especially hear how she pronounces most of her Ts very crisply.  Also, she almost always drops the R at the end or in the middle of a word.  These are two rules to start you out with your British accent.   https://www.youtube.com/watch?v=hNmALFOwqTI 

This is a video of Emma Watson's accent.  It's rather lengthy, but interesting if you want to fall down the British RP accent rabbit hole:   https://www.youtube.com/watch?v=xrWXsoXuuKs