Seriously, what others have said is all great advice.
My list of importance would be:
1) Contact the high school coach, ASAP. Let him know you're interested in making the team next year and ask him what you can do to reach that goal. Ask him if he has any extra time, even if it's after this current baseball season, to help you with your swing, and your game in general.
2) Buy a batting tee. Work off of the tee. A batting tee is the greatest thing in the world and I find that most people don't even use one anymore. That's a sin.
3) See if anyone currently on the team can help you. Tell them you're interested in joining the team next year and ask them to help you with anything you need help with.
By the end of this year (June) you should know where the coach stands on your desire to play, have a contact already on the team, and own a batting tee. This summer you should try and throw as much as possible and work on the batting tee (and know what you're doing, if you don't, have someone (anyone) show you. In the fall, after you've got your swing down from the tee, THEN hit the batting cages and make it a routine(just like your workout routine) to go to the cages.
Best of luck to you.
'When I'm not longer rapping, I want to open up an ice cream parlor and call myself Scoop Dogg.'
-Snoop on his retirement
Your Mom is happy.
A lot of the things that have been mentioned are great, but you can't substitute drills for competition. Find a summer team to play on and see if you still have the desire to play after you finish the season. Sr. Babe Ruth would be a good place to try and hook on. You'll have some ups and downs, but it's extremely hard to go from Little League Baseball to High School Baseball without some type of competition in-between. Play as much as you can this summer. Good Luck.
Talent is God Given: be humble.
Fame is man given: be thankful.
Conceit is self given: be careful.
Hone your defense, or other peoples' perception of your defense. Juan Castro has made a career of it. Speed and defense kept me around through high school, even though I was a terrible hitter.
How do we know he's not Mel Torme?