Hi ridgePO24,
Here, are a few tips to help you start throwing harder:
1. Practice long toss. This will develop arm strength which will translate into faster speeds.
2. Start a weight training program for pitchers. It should focus on all core muscles but special emphasis on legs, triceps and forearms.
3. Practice with weighted baseballs (some lighter and heavier than a standard ball). The plyometric effect will help increase your pitching speed.
4. Get lessons on proper mechanics. I quality instructor can fine tune your pitching delivery and possibly add more speed to your fastball.
Hope this helps,
Jack Elliott.
Baseball Training Tips