This involves (1) using the right sounds to vocalize words, (2) stressing the right syllable(s) and, (3) in many languages, giving proper attention to diacritics.
Ask him to stop you every time you (1) skip a word, (2) read a word incorrectly or change the word order, or (3) ignore a diacritic or some punctuation that calls for a pause or an inflection.