A wedge works by virtue of its shape: a very sharp narrow edge on one side, developing immediately into a broader form. A wedge, metaphorically, then, is a seemingly small advantage that creates a disproportionately large effect. What is your wedge? it could be time management, prose style, or an ability to find the right questions to ask.
In my case, I have an immediate advantage because I have a habit of asking deeper questions of the text. Just being able to read well and develop interesting questions puts me ahead of critics who tend to summarize the text in more obvious ways.