I’m a 16 year old rhp.
Full body static stretch about an hour before game which is a full team activity, as well as footwork and agility drills and run 2-3 laps. On days i’m pitching, 30 mins before game will warm up shoulders really well (arm circles are great), then dynamic stretching, long toss with catcher then throw 15-20 pitch pen. I’m not about being by myself before games i pitch. actually i prefer talking with teammates and coaches and my family to calm myself on the brink of a start.