To make nice thin slices of gravlax, lay it skin-side down on a cutting board. Use a long, very sharp, very thin carving knife, preferably with a hollowed blade. Slice at a low angle from the skin, about 30 degrees up from the table, so that the slices are nice and broad. When slicing, only apply downward pressure when you push the knife, and not when you pull it toward you. Leaving the skin on helps with cutting. Place the flat of your hand on the other side of the slice you are cutting. (Be careful.)