Advice, for those who are interested:
I had to do this stretch to understand how it's done. It's interesting. I did DLD's stretch and moved into Red's. Turns out, I had been doing something akin to Red's stretch in passing.
Anyway, for DLD's scrotum stretch, it seems as though you'll be stretching your balls and penis in opposite directions, on opposite sides. In other words, if you grip your penis' head with your right hand, you'll be pulling your penis BACK toward your crack along your right leg while you pull your balls up along the left side of the base of your shaft.
If you're grabbing your head with your left hand, you'll be pulling your penis back toward your crack along your left leg, while gripping your sack above your balls and pulling up along the RIGHT side of your shaft. If done right, you'll feel it and it won't be unusual or overly awkward to do.
I hope these directions help make sense of the exercise. DLD, please correct me if I'm wrong.
Red's exercise (in my opinion), is simpler to do in terms of direction. Both are powerful.
For Red's stretch, you're simply pulling in opposite directions -- head at 12 o'clock, balls (ball skin) toward 6 o'clock.
My two cents: you might consider wrapping underneath your glans to help grip your penis. Since I was just testing this out, I cut the elastic band from an old sock and wrapped it around a couple of times. This might cause you to get slightly engorged. If it does, unwrap, wait and apply again. (obviously if you have your own solution for a better grip, go with it; I was just curious and wanted to test this out)