Use of space-fillers are the highly unlikely thing that the practice of looking in front of the mirror could correct. Physical traits like posture, excessive hand gestures, and eye contact can be directly seen and practiced in front of the mirror.
Space fillers on the other hand can be practiced when an individual makes a print copy of his/her speech. This way he/she will be guided throughout the speech and the next cues of lines to be said will be easily recovered.