"Dead" and "very" are adverbs of degree used to emphasise the extent or intensity of something. "Dead" is what we would call an ungradable adverb, as it means "completely" or "absolutely". Completely is completely. You cannot be more or less complete. "Very", on the other hand, is a gradable adverb, as it can be placed on a scale to compare the extent of its description with other adverbs of degree. For example, "slightly" and "rather" qualify another verb or adjective to a lesser degree than "very" while "extremely" does so to a higher degree.
In your sentences, "dead simple" means absolutely simple, and there is no doubt at all about the simplicity of the advice (put yourself in the shoes of your employees). "very simple" means to a large extent, the advice is simple to follow.
On a separate note, "dead" is used in more informal contexts. You may have also heard someone saying that he or she is "dead serious". "Dead silence" is another common expression to mean absolute silence.
I hope this helps.