This really depends on what position you want to play. In order to improve your skills you will need help. Practice is the best tip I can provide. You will need to spend a couple hours per day working on hitting high school speed pitches and then you will need to make sure you get fielding practice. Practice makes perfect.
For someone your age there are a lot of options, the first one is to practice, practice and practice. You should also consider talking to the high school coach.
Depends on which position you play. If you are a positional player, practice your hitting, throwing, running and fielding. If you are a pitcher, practice different types of pitches and grips