The very idea of proper pronunciation of Cantonese is controversial, since the concept of labeling native speakers' usage and speech in terms of correctness is not generally supported by linguistics.
[1] Law et al. (2001) point out that the phrase 懶音 laan5 jam1 "lazy sounds," most commonly discussed in relation to phonetic changes in Hong Kong Cantonese, implies that the speaker is unwilling to put forth sufficient effort to articulate the standard pronunciation.
[2] The promotion of proper Cantonese pronunciation is partly in reaction to sound changes found in younger people's speech.
After conducting original research on the pronunciation of words containing these syllable-final phonetic changes, To et al. argue that syllable-final environment sound changes occur due to the tongue position at the preceding vowel, as it opts for maximum ease.
[9] TV and radio programs, including game shows, have been made to promote proper pronunciation.
The proper readings promoted by Richard Ho are based on the fanqie spelling of Guangyun, an ancient rime dictionary reflecting the sounds of Middle Chinese.
He also holds that the flat (平) and sharp (仄) tonal distinction in Middle Chinese is the most important feature from which modern Cantonese should not deviate, especially when reciting ancient literature.
More and more people are pronouncing [n-] as [l-] only because of the bad influences of some language teachers and broadcasters, who inadvertently made the mistake.