I'm going to attempt to answer this question, based upon a limited observation of attorneys. But before I get to that, please realize that the jury trial may be an endangered species. Jury trials are cost prohibitive, often for both parties (one might be unable to afford it financially, others might want to avoid negative publicity, etc), resulting in an increasing number of cases settling out of court.
I was a civil litigant in an Employment Law case. It was very important to me that my attorney possess the "likeable" trait. I have observed him in various situations. He was very likeable, but did not let that stand in the way of doing his job.
I think there are several aspects to this that I observed with him. First and foremost was manners. It is clear that he was raised from a young age to be respectful of everyone, and to treat certain people with deference, such as judges and elders. Definitely watch how you address the jury. Explain what needs to be explained, but don't talk down to them. Watch how you treat the opposing party's witnesses, and counsel. Be mindful that you are being watched at all times, including in the hall, at lunch, etc.
Second, pick your battles. While you owe your client zealous representation, I have seen attorneys object to everything. Everything. If a witness says that Los Angeles is in California, they object. It's necessary to raise every objection to preserve error for appeal, but don't get carried away with it.
Tell a story. Get the jury to be actively involved in the trial, to feel a connection to the case, rather than resenting it as a waste of time.
Body language. Body language speaks volumes, as does tone of voice, and facial expressions. When you need to make a major point by exposing a witness, set it up, get it done, but then go right back to being yourself, without gloating.
Be organized and prepared. Don't waste the court's time, or the jury's time. Be on time!
I think it is really cool that you are doing mock trial!
Keep up the excellent preparation!