Grip: In order to be able to stop a slide it is first important that you are holding the axe in the correct manner.
Hold with the hand over the head of the axe, forefinger along the shaft and adze pointing forwards.
Self Arrest Position: Bring the hand holding the axe up toward the shoulder, letting the head of the axe swivel in your closed fist. The adze should stick into the fleshy part of the shoulder below the collar bone. The pick should be perpendicular to the body. The lower end of the axe should be held with the hand covering the spike (to avoid it catching the snow, or sticking into the body!)
The head should be turned away from the head of the axe, to avoid scratching nose, and to put more weight from the shoulder onto the head of the axe
On The Snow: Aim to get as much weight as possible onto the head of the axe.
Grip the axe firmly, don’t let the adze move away from the shoulder.
Keep the legs apart (making it less likely that you will spin and end up head first).
Keep the feet in the air, especially in crampons, on hard snow, as they may catch the snow and flip you over. In soft snow your feet will be more effective at stopping you than the axe. (see below)
Without an axe: If you aren’t holding your axe or you are in very soft snow you can stop without an axe.
Point the boots into the snow, feet slightly apart.
Gradually push your body away from the snow (as in a press up) so as to bring as much weight onto the feet as possible.