Address your target.
This is where you visualize the successful result of your throw
(Aim high at first)
Extend your throwing hand backward.
You may wish to rock slightly on your back foot.
Then, quickly rotate your throwing arm forward in a large arc.
Be sure to follow-through.
At first, aim high.
After a few practice tosses you'll get used to the release point and you can adjust your aiming point.
UG! Heave that ball!
Too cool! Nice shot!
The white trailing line is 1/8-inch rope, 60-pound test. It is quite light-weight. The tennis ball has been cut open, some sand (or BBs) poured inside, a short length of line is embedded in the tennis ball, and then sealed with silicone glue.
If you are only going to use fishing line, you may be able to get away without weighting the tennis ball. Try it and see! This is fun, and a great way to wear out the kids when setting up for Field Day:
"You kids win a cookie if you can get this line over that 100-foot tree over there!"