Diction can refer to two different but similar things, and I am not sure which you mean.
Most commonly (for me anyway), diction refers to the pronunciation and clarity of speech. Improper diction can involve mispronunciation, as in saying FebUary instead of February or Nucular instead of nuclear, or it can involve poor enunciation (saying words unclearly, "lazy" speaking) as in sumpin for something.
Diction may also refer to the entire structure and art of speech, respecting grammar, word use and order, and so forth (oratory would be a similar word). There is two dogs over there would be an example of improper diction, as would a class presentation that doesn't follow any pattern of thought.. The gettysburg address might be presented as a fine example of diction.
I am not sure which you mean.