You didn't say when the exercise is so, if its happened, hope it went well. If it hasn't, here's another tip.
Try to be your best self and be flexible to the needs of the situation and the group - its how you do what you do, rather than what you do per se which will make a difference. It could be that the group gets messy and confused for example. What they will need is direction, but there are (at least) 2 ways of doing that - grabbing the reins and sorting them out in a controlling way, or helping them stick with the mess and gradually nudging them through it avoiding big conflicts.
It also depends on what you mean by shine - some people polish themselves up and preen, which means they are shiny but don't help the group much and won't get the job; other people can shine by quietly working away to get the group to achieve its objective.
I regularly coach people to help them get in a good resourceful state for occasions just like this so if you want to get in touch let me know. Alan Arnett 07801 340129