Practicing even a “handful” of the 360 possible double-stroke right-hand combinations will rapidly improve right-hand independence and flexibility.
The example below shows the first four combinations, realized on string group 6321:
String groups with an unused string (or two) between “m” and “a” are particularly important for developing strength and flexibility in the weaker (“m & a”) side of the right hand.
Here are the same four combinations on string set 6431:
Experiment with different degrees of separation between right-hand fingers, and also different rhythms, accents, and dynamics.
For reference, here are the 15 possible four-string groups:
Download the PDF below for a list of all 360 combinations: