Videos by Christopher Crowhurst.
Though these were shot in a pool, and make rolling look more like flashy art than useful utility, I guess the best takeaway is the relaxed ease rolling requires.
First step to rolling is feeling unperturbed while upside down.
In a pool, freshwater-filled nasal passages make rolling practice uncomfortable. Consider nose clips, a diving mask or, most simply, a steady exhale through the nose.
Also consider that the tulik favored by Greenland rolling purists looks a little dorky. And should you have to wet exit, you'll have to self-rescue wearing an enormous skirt that's ungainly and cumbersome.
Nose clips from Amazon. Also, Kodak's really well-reviewed waterproof HD videocamera - I have great luck buying them refurbished.