Adult learners work out the pronunciation of new words by mentally reading the words. They focus on spelling rather than on sound. The process is more visual than auditory. The problem is that you are very likely to read out and say words in the way the phonemes are pronounced in your first language. This leads to problems in pronunciation that may eventually become chronic if not corrected.
Learners who acquire vocabulary through reading - this is especially true for people with a more technical background and all their technical literature - sometimes show good structure and syntax skills and can be quite coherent in their discourse. However their overall speaking is affected by the mispronunciation of key words, which in turn hinders effective communication.
What to do then?
It is necessary to bring the process from visual to auditory. Before worrying about the spelling of a new word, you should focus on the way it sounds and try to reproduce that sound. It is necessary to have at least some oral practice before getting into spelling. That will not guarantee correct pronunciation, but it allows learners to first be exposed to way a word sounds. Spelling has to be shown and dealt with in a second moment.
Accurate pronunciation of sounds is only one aspect in the process. Syllable stress, sentence word stress, sentence intonation and speech music will also affect the way you sound.
I still recommend the technique even though it doesn't seem to work very well for Inspector Clouseau.
