Naturally, it shouldn't look rehearsed, but rather, prepared . And I would also disagree that you can't follow a plan. During direct examination, notwithstanding some sustained objections for opposing counsel, you can nicely follow your plan. In the biggest trial in which I ever participated, I actually had a script with the attorney's questions and my answers written down verbatim. Naturally, these were the answers I had worked out at previous meetings with the attorney.
Football games are even more unpredictable than trials, yet they have plans too.
This is made worse when they don't even really understand the subject matter. Most can't even locate their anatomical hips or shoulders, so get them involved and interested by using props to make your points. The courts generally allow you to make use of illustrative evidence to facilitate understanding, by the lay jury, of potentially complex and technical issues. These are essentially legal tests for scientific testimony. In Daubert, the U.S. Supreme Court essentially dismissed Frye, promulgating fresh standards of scientific critique.