About to face arena gauntlet

My group is about to face justice for a minor crime by fighting in an arena. Pretty excited and nervous about it. I'm at level 5, and I believe the rest of the party (players come and go so it's not very consistent) is at a similar level.

Any advice from veterans for surviving in such an environment? I'm considering arranging the party into ranks (warriors at the front, healers in the middle, casters at the back) and using what illusion magic I have to manipulate the battlefield. Any useful knowledge or strategies would be very much appreciated, at this point.