What is the primary cause of Fly Aways? Are there steps to take that can eliminate this risk?

(#1?) Probably human error and failure to follow procedures and ignoring signs of trouble (been there, done that).

Not calibrating the imu and compass are the main causes.

I've also noticed that a good percentage of these flyaways are happening to people who haven't owned the drone very long, they don't read the manual, they don't know about return to home or that they can follow the little arrow back on the google map and it  gets out of site and panic sets in.

Not always the case,I have two s900 and feel I'm pretty experienced,last year while I was in the garden hovering the inspire to drain the battery,the craft just went mental flew away no response to any control or rth,flew 300 meters down the road and crashed into a neighbours fence at 48 mph,sent to Dji and they gave me a new inspire my rma stated a battery fault! Yeah right!!, still have no real idea what happened,just know something was as fault with the inspire as they replaced without question?

Follow the instructions and guidelines.
Read DJI Tim's tips common pilot errors posting.
The only way avoid risks it to keep the aircraft on the ground

Rich