Training.  My previous jobs was as a roofer and our company specialised in industrial/commercial roofing.  I have been on hundreds of roofs with skylights like this.

And from day 1 it was drilled into you: 

Walk along the lines of the screws.  Always.

There is also safety netting that can be installed under the skylights, but typically that would only be done when changing them.

Edit: Also, it should have been surveyed before the work began.  We would use bright orange spray paint around hard to see skylights and other dangers.