I was presiding at piano in a 13-piano-ensemble at The Cemetery for Martyrs in April 2006.

Please give me some advice,thanks!

I was presiding at piano in a 13-piano-ensemble at The Cemetery for Martyrs in April 2006. It was a successful performance, but it's not the performance itself that impressed me most, but the previous time of rehearsal. The ensemble needed everyone's cooperation on attitude, time, and practice. But accidents happened a lot: someone got sick, someone had a meeting...so that the rehearal kept being tough. The music teacher was angry and blamed those who were absent, making them embarrassed and frustrated. Being the leader, I comforted and encouraged them; I collected all their schedules and rearranged a new rehearsing time, making sure of everyone's presence. The rehearsals were not smooth for the long and hard melody as well as the high playing requirement. I appeased and inspired every player who ever wanted to give up for I knew that only the union of excellent individuals could bring their potential into full play. And finally everything just paid off. I think I would remember this time forever.

You are answering the prompt with what is essentially a very short story, which is good. However, you give away the ending in the second sentence, which is not so good. Also, most the story boils down to a list of things you did to help make the project successful. You might want to add a personal element, maybe talk about what the experience meant to you, how the experienced changed you, that sort of thing.

Better to write out the numbers, so it looks nice:

I was presiding at piano in a thirteen-piano ensemble...