The teaching methods that I use vary depending on the linguistic background of the student. In order to achieve an authentic British RP accent, there are various aspects that we have to consider beyond just pronunciation and phonetics.

The problem that many students will face is the physical mechanism, the mechanics of how we create sounds. You will often hear people say that the RP accent comes from the front of the mouth. In other words, you can hear this strong aspiration of air coming out of the front of the mouth as each syllable is articulated. 

But the question we have to ask is how is this achieved? You see, most phonetics books will focus mainly on the positioning of the tongue when it comes to articulating the sounds of English and for many students, this will probably be enough. 

If I'm teaching a student from a General American English background, most of the focus will be on avoiding rhotic sounds, lightening the /l/ sounds and making some slight adjustments to the vowel sounds. After all, British English and American English are both English. The aspiration and syllable stress and rhythmic patterns between the two accents already share much in common. In this simplified example, making adjustments to the positioning of the tongue and the shape of the mouth can result in a natural British English pronunciation.

You see, the subtle mechanism by which we create sounds varies among the languages and this is influenced by the oral cavities from where the sounds are aspirated. Some languages can be more guttural, some languages can be more nasal, some languages can sound higher pitched and other languages can be lower pitched. This goes beyond just the positioning of the tongue and this is why so many non-native English speakers struggle to attain native-like pronunciation when speaking English.

We also have to consider the rate of airflow which can affect syllable stress. These are aspects that go beyond the simple placement of the tongue and when students try to apply the same mechanisms of their native language to that of English, they run into problems. The British tongue does not move in rapid succession in the same manner as a Spanish, Italian or Japanese speaker. In English, the articulators make deeper contact for mere fractions of a second creating more resonance between the articulators. Once a student can understand the interrelation between, the lungs and aspiration, they will make good progress.