Here is what you need to do...
The first step to throwing farther is by judging how far along you are with your throwing motion. If your mechanics are poor then you may not be seeing the results you are seeking. Now considering I was never a quarterback I would highly recommend you looking online at a website such as youtube to watch videos about proper throwing motion.
Now that you know what a good throwing technique looks like video tape yourself. You can have your friend of family member record you as your throwing to someone or just throwing the ball to a target. Now that you can look at your own throwing motion. You can compare it to the other video that shows proper technique. If your form looks good then you should continue to the next step, if not work on your motion because that is more important than the next step. Once your motion has became good you should continue to the next step.
Once your throwing motion is good you should supplement throwing practice with a form of weight training to help develop stronger throwing muscles. You should focus on your shoulders, and deltoids. You should do movements such as shoulder presses, lat pull downs, and bent over rows. These movements will help to develop stronger throwing muscles. You shouldn't just plan on lifting continue to work on your throwing motion as well as lifting.
Difficulties people often experience or parts that need special attention to do it right.
Throwing motion is much more important than lifting in my opinion. With a good throwing motion you can limit injuries and learn the right way of throwing.
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The Student Author's Background
Funny or interesting story about this topic...
When did you first do this & how did you get started?
I could never throw a football very good. I never played any position regarding to throwing the ball but once I started high school I learned how to throw the ball properly, and developed throwing muscles.