Maybe you only have the one hand. Maybe you want to show off. Maybe you're just too cool to deal cards with both hands. Whatever the reason, this is a skill that will elevate your status from card player to master card manipulator. Okay, maybe not. Still, it's fun to do.
(See the youtube video clip)
Step 1: Mechanic's grip
The thumb rests across or near the upper left corner of the deck. The index finger supports the cards by the top edge of the deck, and the remaining three fingers grip the deck on the right edge.
Experiment with the vertical positioning of the deck. Initially, I tried holding the cards closer to the top edge, so that the lower right corner of the deck stuck out of my hand. I later found that I was able to get more leverage on the cards (later steps) when I held it in a normal mechanic's grip (dealing grip).