I have a very strict rule in my life. My girlfriends must be able to sling!

Aside from a few girlfriends, I have also taught a few male friends.
My aim is to teach them how to sling in helicopter/sidearm in a general direction. It's just a relief getting them to this skill sometimes!
My recruits have an uncanny ability to possess beginners luck. I stand about 10-15 meters away and instruct them to sling a tennis ball to me lightly. To my consistent surprise the ball almost always flies straight into my hands the first few times.
(Very frustrating - I was never this good in the beginning!

)
Afterwards I increase the distance, usually to 30 meters or 50. I instruct the recruits to aim between soccer goal posts; accuracy decreases quickly
However, after an introductory class my recruits aren't so eager to continue practicing. It takes a certain type of person to hold an interest in slings. And exceptional people to push through certain failure to achieve accuracy.
Ps. Teaching slinging makes a really fun action date!