Creating the legitimate reputation of being an expert in a specific area is difficult. This is because the amount of literature available in any area of expertise --- however obscure --- is massive, and that is just the material available in English. In addition, there are many people, perhaps too many, holding advanced degrees in nearly every important field in the English speaking world. As a result, competition is immense.
Instructions
1. Choose your area with care. It should be highly specific. It cannot be something like American history, as this is far too broad. It should be more along the lines of the political thought of the antebellum South, or the economic history of Midwestern agriculture in the 20th century. Only when the field is described like this can you reasonably have the chance to grasp the literature in the field. Even with these focused descriptions, the literature will take years to digest.
2. Set intellectual parameters. Lets say you choose the political thought of the antebellum South. This does require you to read the major fiction writers of the era, newspaper articles from the time and the clearly political writing of southern authors. You cannot avoid this; they must be read and understood. On the other hand, getting deep into the economic theory of plantation owners might be irrelevant. You are not required, in other words, to study an area like the antebellum South from every disciplinary point of view. You are, however, required to study every conceivable source of political ideas from a) that area, an b) that time period.
3. Read the main book titles in your area first. In every field, there are a list of big names that have made a large impact in the area. These must be read with care, and all major arguments teased out.
4. Read the more minor books. Often, these books are meant to take issue with the main works in the field, or to add more information to them. The minor works will always reference the major works constantly, and they often assume your knowledge of the major arguments, evidence and theses.
5. Read related articles. These should be peer-reviewed pieces in the major journals. It is always a good idea to keep a notebook where you record the author, title, date and main argument of everything you read. You can then refer back to this and see how the different sources relate to each other.
6. Keep track of updated information on the Web. Not everything worthwhile is peer-reviewed. Many websites in a specific academic field are run by real experts and treat their material in a highbrow manner. The Web is what people want to read. The truth is that academic sources are read only by other academics and --- with the occasional exception --- are unknown outside that narrow specialist community.
7. Go beyond the specialist community. Academia is a distorting environment. It encourages in-group thinking and intellectual conformity. Being sequestered in this tiny community can do as much harm as good. There are many in the broader community that are just as knowledgeable, but somehow live without tenure. There are many resources outside the academic field; these should be used as balance. In addition, this might also serve to differentiate you from the more strictly academic experts in the field.