The ability to articulate your background is a combination of good preparation (which you have full control over) and vocabulary/enunciation (which you have practiced control over). Your "smartness," "sharpness," "quickness," "aggressiveness," and "brightness" are all attributes that are evaluated based upon your verbal articulation. If you have "lazy lips" you may want to practice enunciating and forming your words more clearly. And whatever you do, don't continually reach for elusive words to perfectly portray your thoughts and feelings. Any practiced interviewer prefers an individual who is comfortable within their vocabulary level than one who is always searching for obscure words at the level above.
In practicing your articulation, take careful note of the "quickie" words which we tend to develop in our everyday speech pattern. Words like "gonna" and "yeah" and "y'know" and "kinda" are all interview stoppers. They can make you sound uneducated and coarse. And they have a habit of repeating. We have all probably had a parent (or sibling) point out the use of "y'know" in our speaking. In addition, you may have particular words or phrases you use for emphasis which can become particularly pronounced in the interview. These would include "to tell you the truth" and "truthfully" and "basically" and "OK, well" and "Like…" As a side note, I once counted the number of times a candidate said "to tell you the truth" after it became particularly repetitive. She said it over fifteen times. And I began to question her truthfulness.
Use words you know and with which you are comfortable. Don't use words you think I think you should know.
Make sure you are fully prepared for the interview, reviewing both your own background (nothing will kill an interview quicker than someone who cannot recall personal events) and the background of our company. Proper research will help you articulate your answers in a clear and succinct manner.