Two things stand head and shoulders above all the rest for me:
(1) Whatever you do, do not slack off academically in your senior year. Admission and the accompanying grant-in-aid are conditioned upon satisfactory completion of the high school curriculum. I know a very fine player who, after slacking off in the first semester of his senior year, received a call from the college's head coach; telling him that his admission was now provisional. Instead, he'd have to pull a high GPA in his remaining high school semester and in a local college's summer school before he'd be allowed to enroll and join the team. As it turned out, he took it to heart, made good grades from then on, and ended up having a very fine career; both baseball-wise and academically.
(2) Show up for fall baseball in the best possible condition; rested and ready to go when you arrive on campus in August. The rigors of fall baseball and college academics, combined, can't be over-emphasized. In fall baseball, you're competing against 34 other studs for playing time in the spring; and many of those teammates against whom you're competing have one or more seasons of college ball under their belts. If you show up tired from too much play in the summer, you can't do your best; and your best is what it's going to take to break into the lineup or rotation. Meanwhile, you're probably going to be asked to apply yourself academically more than at any other time in your life. The last thing you want to do is to be anything less than 100%.
Congratulations to those of you who are verbally committed at this point! You've worked hard for what you've achieved and can look forward to baseball at a whole new level.