Here’s a great way of approaching double strokes. Rob Knopper explains a method to help you develop “machine-gun” doubles. In other words, a very even sounding double stroke roll. You need to figure out for yourself how you’re going to get the second stroke to be louder than the first.
My doubles came together when I learned to use my middle finger as a spring. I can also use my fingers to help as well as a little whip of the the hand. This subject in particular makes me think about how I’ve used a bunch of different techniques to develop my double stroke roll and I’m not sure which of them is the most effective.
With my students I work first on a 2-for-1 rebound that works with a middle finger fulcrum acting as a spring, “squeezing” against the stick. This is the method taught by the venerable Murray Spivack and passed on by Chuck Silverman and Chad Wackerman (who’s masterclass on the subject of snare drum technique on Drum Channel is alone worth the subscription charge). Then we might evolve to using a Moeller whip-type-thing or finger snaps/ open-close/ push-pull. All drum techniques are the same in the end.
Watch and learn from this very informative video.