James Han, chef of Wild Fish in Seattle, teaches Sushi Monsters how to cut and plate sushi rolls! More info at http://www.sushimonsters.com

Kampai Roll: Spicy salmon over shrimp tempura and avocado.

Find a sharp knife and cut the roll all the way through, into individual pieces.
Experiment with different cutting orders and methods to find which works best for you.
Serve your sushi on a plate.
For less fragile rolls, pick up the sushi with both of your hands. This way, you can easily plate the sushi in a U shape or another shape with curves.

Tornado Roll

Here, the chef is cutting the sushi in half each time. This may eliminate the problem of ending up with two many pieces in the end.
When plating fragile rolls, grab the pieces one by one.
Arrange them on the plate in a staggered way.

Lion King: Spicy crab over shrimp tempura, avocado, and tomato.

The salmon is being seared.
Sushi roll pieces vary in width, but making each piece a little under 3/4 of an inch is a good place to start.
Picking up the roll at once makes curving the roll on the plate easy.
Tasteful application of sauces and garnish helps with presentation as well.