One analogy I often use when coaching clients to develop the proposal is that of building a house. The proposal represents the foundation or "frame" of the house, and, as such, needs to provide a sturdy foundation for the upper floors (data collection, analysis, reporting). Often, many dissertators try to write the first three chapters in order- chapter one, chapter two, chapter three. I don’t recommend this. The first place to start is to think about what your finished (dissertation) will look like. What will the dissertation show? How will it add to existing literature?