I had fun drilling belly rolls today!...
contract upper abs, release, 30 times
contract lower, release abs 30 times
alternate contracting upper and lower abs, (i.e. contract upper abs, release, contract lower abs...)
Now smooth it out into a bellyroll! Bellyroll 30 times
Make sure to roll your belly from top to bottom, and bottom to top! (and maybe side-to-side?!)