This is the way it has always worked best for me when it comes to Leatherman can openers:

Can in left hand, can opener in right hand. Place can opener on right-side edge of can. Leverage can opener while turning can in a counter-clockwise direction.

Now, for swiss army knife can openers:

The blade portion of the can opener is on the front, so it seems to work better turning the can in a clock-wise direction. Still holding the can in the left hand, can opener in the right, placing the opener on the right edge of the can.

Basically, I always hold the can opener in my dominant hand, can in my non-dominant hand, place the can opener on the side that is easiest to reach with my dominant hand, and turn the can towards the sharpened edge of the can opener.