There are several kinds of falls. The most prevalent one is when you lose hold of the rock and gravity accellerates you at 9.81 m/s^2 towards the center of gravity of the planet. The others I'm less familiar with.
Not much you can do in the air. When you fall, it tends to happen quickly. Fall only if the fall is clean. If the fall won't be clean, don't fall. Oh, and don't fall on ice, don't fall on low angled terrain, don't fall when there's bad pro, don't fall when you'll go 100 feet, etc, etc. And since you seem to want to alpine climb, focus on not falling in general.
As for the rope/leg issue, think about what will happen if you were to fall. It's pretty simple. When you're above the pro, rope between your legs. To the left, the rope should be to your right. And vice versa. Visualize the fall, and you'll see if the rope position is correct. It's not rocket science.