Most people who end up getting hurt with these are because they are full of fear. They tighten up and anticipate the impact and end up fighting gravity the entire way down and splat onto the mat. Instead, they need to relax, stay calm and think more along the lines of welcoming the mat with vigor.
I remember hearing about a study of cats with broken legs from falling various heights in which there seemed to be less chance of injury on slightly higher elevations than some lesser heights. The reason given for why was that initially cats tended to tense up in anticipation, but past a certain height they had enough time to begin to relax.
Creating larger surface areas during impact and translating down momentum laterally is my basic approach. If I'm rotating through the air I'm basically expanding my limbs to eat up momentum, which also facilitates reaching for the ground to help control the way my body moves as I land.
How not to land
: no purposeful/meaingful lateral rolling of kinetic down force.