It is often useful to explore and play with the opposites.
For the rider, use over exaggerating to help find center.
Here are a few ideas:
Twist your belly button right, center, left center, repeat to help yourself feel the two directions and find center.
Look over your right shoulder, center, left shoulder, center and repeat if you tend to look to much one way
Tilt your head right, center, left center
Tip your body forward (like hinging from the waist), center, back, center and repeat
Collapse your waist right, center, left, center
Lift your knees up and down to feel when your leg is gripping.
Get creative! The possibilities are endless!
For more exercise ideas, check out Dressage To Go, the app for on demand audio lessons to level up your riding.