Ski faster. Do NOT, NOT use dish soap or any other product. Do NOT wipe the inside while they are wet, damp, or fogged. Good quality ski goggles have a film on the inside that gets soft when damp, absorbing the 'fog'. If you've wiped them, or god forbid, used soap and wiped them, they are ruined. Get new ones. Keep them off your face while hiking or skiing slow. Do not get the inside wet with snow or water.
If you fall while skiing I know some park skiers carry an extra pair inside their jacket and swap them out.