I often get to watch Karate demonstrations, whether live or on DVD (or some other medium). I have much to learn myself, but I can suggest two things that will greatly improve many students' performances:
Slow down. Don't rush the count. Take a walking pace between movements and then move quickly once you get there. Give yourself enough time to "set" your movements. There is no need to hurry.
Lower your shoulders. The excitement of being in front of a crowd or camera often makes a student nervous and tense. It shows in the shoulders. Your shoulders should always be pressed down. That is a basic thing -- but it took me more than 20 years to begin to get it. Power comes from your entire body. It goes through your shoulders. If you raise your shoulders, the power will be blocked, slowed, and/or lessened.On the rare occasions when I have given public demonstrations, I have done both of the above improperly.
Slow down and relax.
Charles C. Goodin