Your research question is the most critical part of your research proposal -- it defines the proposal, it guides your arguments and inquiry, and it provokes the interests of the reviewer. If your question does not work well, no matter how strong the rest of the proposal, the proposal is unlikely to be successful. Because of this, it is common to spend more time on the researching, conceptualizing and forming of each individual word of the research question than on any other part of the proposal.
To write a strong research question you will need time. Step away from your computer; consider what drew you to your topic. What about it animates and matters to you? Listen to yourself and start formulating your question by following your own interests. Remember, you will spend a lot of time researching and writing about the proposed project: if it does not interest you in the beginning, it will certainly become very difficult to write about in the end.
Next, extensively research your topic. What have people said about it? How have they framed their research? What gaps, contradictions, or concerns arise for you as you read, talk to people, and visit places? After you have done this you can go back to your computer or note pad and start crafting the question itself. When you do, consider that a strong research question should be evocative, relevant, clear, and researchable.
The Research Question Should Be Evocative
Evocative questions are ones that catch the interest of the reviewer and draw her/him into the proposal. Equally important, they easily adhere in the reviewers' memory after reading the proposal. Questions tend to be evocative because of the ways they engage with challenging topics: they pose innovative approaches to the exploration of problems, and because of this the answers found are far from obvious. There is no single way to form a conceptually innovative question. However, some of the following qualities are common to successful proposals.
Make it timely. Evocative questions are often distilled from very contemporary social or theoretical concerns. For example, questions regarding the energy crisis, international tribunals, nationalism, or the rise of anti-globalization protests are likely to peak the interests of others because they are questions whose relevance will be clearly discernable for reviewer.
Frame it as a paradox. Frame your question around a provocative paradox. For example, why have indigenous organizations in Bolivia markedly declined while the number and quantity of funding sources has increased? Or why have violent conflicts over forest resources increased in the last ten years while the very people involved in these conflicts have become less and less dependent on forest resources for their livelihoods? There are many potential answers to these questions, and your research may ultimately challenge your own expected explanation -- but this in itself is a relevant discovery. These types of paradoxes pull the reader into the proposal and set up a situation whereby the research will fill in a provocative piece of the puzzle and make clear a much-needed broader understanding.
Take a distinctive approach. Finally, a question that approaches an old problem in a refreshingly new way, or proposes a surprising angle of analysis on a difficult dilemma, is likely to prove evocative for reviewers. This could involve a new methodology, a new conceptual approach, or the linking of two previously disparate fields of knowledge. These innovative approaches both develop confidence in the intellect of the researcher and hold promise for new understandings and insights to old and difficult questions.