Though they may be some of the strongest teammates in DC Comics, The Flash could teach Green Lantern a thing or two about how to use the power ring as an effective weapon. During a Flash and Green Lantern team-up in DC Comics, the Scarlet Speedster proved that all Green Lanterns are using their rings completely wrong. This story was told in The Flash Annual #2, which was part of the New-52 reboot and came out in 2013. The issue was written by Brian Buccellato and illustrated by Sami Basri.
The story starts with The Flash and Green Lantern suddenly transported to an alien planet. Years earlier, at the start of their superhero careers, The Flash and Green Lantern first met while separately investigating the abduction of missing children. It turned out they were being taken to this alien planet to be trained as fighters in a death match. With their powers weakening, the only way off the planet was for Green Lantern to cut a deal with the aliens that the two of them would one day return to the planet to compete in the death match themselves. The story then jumps back to the present, where the aliens have taken Flash and Green Lantern for them to make good on their deal.
The death match starts off with a battle royale, with The Flash and Green Lantern easily defeating their opponents. But only one of them can take on the champion, so the aliens restrain Green Lantern so that The Flash can fight him by himself. Seeing The Flash in trouble, Green Lantern authorized his partner to use his ring. The speedster utilizes it in a way the Green Lanterns could never: he uses his speed thinking to get an instantaneous crash course on how to use the ring. Then, using his speed thinking again, analyzes his opponent to learn his weakness. Surprisingly, the answer is to shoot him with an energy blast to the crotch.
While The Flash had the Speed Force to help him out in this scenario, he still showed that the Green Lanterns have not been using their rings to their full potential. Green Lanterns, and Hal Jordan specifically, make big elaborate constructs to fight their enemies. Barry Allen, on the other hand, just ended a fight with brute strength straight to his opponent's “weak” area.
Any Green Lantern fan will know that the rings work on willpower, as the opposite of fear. An interesting tidbit to the story is that the ring recognizes the Flash as being able to use it because he can “outrun great fear.” So it’s good to know that in a pinch, Green Lantern could let The Flash use the ring again, as willpower and super speed is a great combination.