Creating effective displays, though not rocket science, need familiarity of elements and principles of design.
However, at times, this is not enough. It also helps to take into account customer sight lines. Regardless of how attractive and how much you have successfully implemented design principles, your display is rendered ineffective IF NO ONE SEES IT.
No one walks with their head tilted up to the ceiling. Well, er, except me because its my job to take note of shop design and displays.