[C_F_H_13]

Here's a great one I stole/borrowed from a video I saw.

1. Play alternating 16th notes with both hands and feet in unison. Do 16 bars
2. Switch hands to parrididdles while keeping feet alternating L/R. Do 16 bars
3. Switch Feet to parrididdles and hands back to alternating L/R. Do 16 bars