Begin with fundementals. It is a recurring theme of mine but you can’t emphasize them enough at this age. Make sure he throws the ball in a fundementally sound fashion, make sure he does it regularly. If it isn’t regular (Say only game day and the odd once before the season practice…for example) it will be nearly impossible for him to have a high % of strikes. With just those 2 things; practicing fundemental throwing, with regularity, I would contend that he has an excellent opportunity to develop into a sound and healthy pitcher. I see many kids attempt to emulate what they see on MLB games and they end up throwing in an uncoordinated or posturally incorrect or arm unhealthy manner, backing it down to simple efficient athletic movements is much easier for the kid to handle and understand physically so throwing to a spot is much more regular.