Cut the fish down the belly to the, uhhhh, butt. Scrape out the gutso's.
Chop off the head (or keep it on until later to get a better grip, whatever you prefer).
Insert the knife just above the center line of the back of the fish. Run the knife all the way down to the tail.
Continue running your knife through the fish and create your first fillet. At about the center of the spinal column, you can pull the fillet up to release some of the bones that stick up into the fillet, then continue to slice till you get to the base of the fish.
Flip your fillet over and this time start at the tail and work your way up.