Take Your Medicine Balls
There might not be anything out there that gives you as much bang for your buck as medicine balls. Every sort of movement that an athlete should be getting better at can be trained using medicine balls. In addition to that, anti-movement training, or stabilization exercises, can also be done with medicine balls.
Medicine balls come in many shapes and sizes and you should have several variations to provide training versatility. Throwing medicine balls, slamming medicine balls, and using them to add resistance to core workouts are all ways to use them effectively.
In baseball we want to strengthen ourselves in several dimensions, including rotation. We need to get outside of the "straight ahead power" mode from time to time and strengthen our core, back, lats, and enhance our ability to stabilize ourselves while in explosive and/or rotational movement.
If you're not using medicine balls in your workouts, you should start right now. They're inexpensive for the amount of workouts you can do with them, and the benefits they provide are perfect and many.
You can throw medicine balls in a variety of ways to strengthen your body, you can use them with a partner or without, and you can even throw them off mini trampolines. We'll detail a few workouts in particular as we go on our website, and we suggest looking at this tool for strengthening the core and lats in conjunction with your medicine balls.
The hammer net allows you to put any medicine ball that you own into the net, and slam it into the ground. Overhead chops, side to side slams, any kind of motion you can think of. We have also spun like a hammer throw and flung the ball across the field using the hammer net. There are dozens of ways to use this tool to improve your fitness.
There is also a less expensive slam net on the website that is use able but little less durable. It basically just depends on how much weight your planning on putting in the net.
These are great tools because they allow you to hang onto the ball through the slam, and train "change of direction" strength over and over.
Check out Eric Cressey's High Performance Handbook for help developing your own personalized fitness program.