There must be something that you are passionate about but not enough answers available. The more the dilemma persists, the more relevant you can research and give us better answers.
A thorough and in dept diagnosing and analysis of the research problem and the methodology to be adopted in moving closer or proffering an outright solution to the problem identified constitute the bases of Research proposal.
The goal of a research proposal is to present and justify the need to study a research problem and to present the practical ways in which the proposed study should be conducted. The design elements and procedures for conducting the research are governed by standards within the predominant discipline in which the problem resides, so guidelines for research proposals are more exacting and less formal than a general project proposal. Research proposals contain extensive literature reviews. They must provide persuasive evidence that a need exists for the proposed study. In addition to providing a rationale, a proposal describes detailed methodology for conducting the research consistent with requirements of the professional or academic field and a statement on anticipated outcomes and/or benefits derived from the study's completion.
I agree with all of the previously mentioned points about the essential elements in the content of research proposals. But I think it is also important to get the writing style and vocabulary right. The content will certainly be the ultimate deciding factor but making the proposal look right helps persuade the evaluators. It has to meet their expectations for how a proposal should look.
These expectations may vary across different fields and even for different evaluating bodies. Therefore, it is important to follow the guidelines for that particular proposal (if available) and to find examples of proposals that have been successful. Not to copy the example but to learn about the layout, style and language used. Following a similar pattern can be helpful in meeting expectations.