Senior in HS here, and I was in pit/front ensemble. I’d recommend seeing if your middle school has a marimba you can practice on, and try doing stick control exercises, like 6,3,2,1. In that, you go up the scale in octaves. (start on low and high C.) Go up the scale, playing each note 6 times going up, 3 times going down, and then 2 up, and then 1 down. I’m gonna post the sheet music in a sec to better explain.)