In an avalanche, never give up in terror. Keep fighting. They usually happen in fresh snow or recent snows. Be aware, prevention is your best defense. Certain areas are more prone than others. If a slope does avalanche there will be a fracture suddenly working its way across the slope with muffled detonation and a whole layer of snow peeling away.
In response you should:
Get rid of ice axe, poles, skiis, or any object that you are holding immediately by throwing it away from you. Quickly check if at top, center, side, or bottom end of fall.
Dive for the best escape at top or sides if possible.
At all costs try to delay downhill slide. You can do this by leaping upwards if avalanche breaks off by ankles, or to one side if you are near solid snow, or by clinging to some bush or rock horn sticking out of the snow. The less snow above you, the less to bury you later.
Keep mouth tightly shut. Swim.Try swimming for side. Use a sort of double-action back stroke with back to force of avalanche and head up. If in danger of being clobbered by solid slabs of snow try rolling into a ball. There is no cut and dried answer. Ride it out as best you can. But keep your mouth shut (many avalanche victims die from drowning with snow melting into lungs).
Reserve greatest effort for last few seconds.
Bring arm up in front of nose and mouth.
When avalanche stops make one huge effort to break out. As avalanche loses momentum and starts to settle, two things are paramount; an air space in front of face and being as near as possible to the surface. In that last final effort, if you don't know which way up you are ...spit. Then follow the direction of the saliva, backwards.
Don't panic when trapped. Easier said than done. Fear uses up oxygen by faster breathing rate and you want to conserve as much oxygen as possible. Try hard to keep calm. You can survive underground for hours until rescuers arrive.