Writing a dissertation proposal is possibly the hardest part of the dissertation writing process. In creating a dissertation proposal you are crafting something out of nothing. Developing an understanding of an issue, identifying, reading and summarizing the relevant literature, and developing your own take on the problem are time consuming and no doubt is a frustrating process. In many ways the dissertation methodology is the easiest part to develop. Once you have a clear idea of the first pieces, the methods should follow easily. Which helps you to answer the question, how to write a dissertation proposal.
Basically you need to introduce your work. As a rule of thumb, your thesis should cover enough ground to be worthy of three conference papers. Organizing your thesis around three conference submissions may help you progress toward your thesis (it gives you hard deadlines).
Your list of contributions is the most important part of your dissertation research proposal. This is where you succinctly outline why your work is different than other work on the subject, and why it is worthy of a Ph.D. thesis. This is traditionally in a bulleted list, and should probably be less than a page. It's worth really working on these contributions, because people will inevitably ask what your thesis is about, both in the lab and at conferences. You should be able to give an answer in few seconds, and that answer should come from your contributions page.
You should remember that you are proposing something new. Sure It doesn't have to be complete but It's probably somewhat better if it isn't complete, because it shows that you can talk intelligently about what work you plan to do before you do it. Here is a standard dissertation outline
a. Summary of the larger puzzles and issues
b. Locating your work in a larger issue
c. Main research question
2. Problem Statement
a. What is the issue?
b. What are the specific questions?
c. What is the context and background?
d. Why does this matter?
3. Conceptual Framework
a. How do you look at this puzzle?
b. What is the theoretical framework (what is this a case of?)?
c. What are the key constructs?
d. What are specific terms you are using and how do you define them?
e. Model of what you think is going on
a. What do you plan to do and why
b. How do they link to the questions and the CF?
a. Survey drafts
b. Pilot data
Therefore a properly written proposal must demonstrate that you:
1. Able to explain the importance of the problem issue to a person no familiar with it;
2. Have managed to define and delimit and interesting and fascinating research question;
3. Able to formulate testable hypotheses;
4. Have worked out a detailed plan that will test your hypothesis.