Center your thesis around challenging an existing idea or theory from a particular author or school of thought. Break down the arguments that support the idea or theory in question and, if possible, provide an alternative approach. Merely dispelling a certain belief is a sufficient achievement for a master's thesis, but it will be even better supported if you suggest why the evidence supports another idea. For example, an MBA thesis could break down the logic of Garrett Hardin's notion of "The Tragedy of the Commons" and suggest a new idea based on modern theories of human motivation.
A master's thesis can display mastery of the subject by conducting an extensive study on a specific primary source or sources that have, perhaps, been under-researched. You must access these sources, or copies of the sources, directly to meticulously explain and provide insight into them. From this point, elaborate on the meaning of the primary sources and what they imply for the academic field to which they belong. Some such primary sources include historic diaries, complicated government legislation and census data.
Focus your thesis around a particular secondary source and the ideas of its author. You can elaborate on the ideas within the source and explain where the author "got it right" and where he "got it wrong." Provide historical context from the time the source was written that may give insight into the author's mindset. Explain how the source is relevant to today's world and its impact, if any, on the academic field of study to which it belongs.
Conduct original research to support an existing concept or to showcase a new idea. Original research involves a first-hand study, in the form of surveys, interviews or polls that provides completely new data on a particular topic. Analyze these data for any possible insights they have into a certain field of study, while also discussing their possible failings. Support your original research with primary and secondary sources to provide context for the data and create a more well-rounded thesis.