The first thing to note is that a proposal is not an actual paper, but instead is a preliminary discussion of what you will include in a longer paper. To start work on a proposal, the first thing you need is to narrow your focus. You might choose to write about the business cycle in one type of industry, such as copper mining or or medical technology, and show how a small group of firms in that industry have gone through one complete business cycle. Another possibility would be to focus on a particular region, looking at, for example the rise and fall of cities such as Detroit as part of the business cycle of the automotive industry. Once you have chosen a particular business cycle to research, writing the proposal is fairly straightforward.
Many proposals are written in a fairly standard format, in which they include a summary of your major argument, an analysis of existing scholarship, and then a detailed outline of the complete paper. Your syllabus or assignment sheet should contain details on what the instructor wants to see covered in the proposal; the key to success in this sort of assignment is following your instructor's instructions closely.