Open with an explanation of the purpose of your research. Start by explaining why your research is useful. Generally this section will simply include how your specific research will advance understanding in your subject area.
Explain what compelled you to study the issue. Provide an anecdotal explanation of what drew you to the specific area of study, explaining how you came up with the idea concisely. Avoid going into too much detail in this section as conciseness is key.
Demonstrate an understanding of the topic. The dissertation committee wants to see that you already have some knowledge. Explain to them what you already know, showing them that you have a sound enough base in the subject area to allow you to delve deeper into the topic that you have selected.
Predict some logical questions and prepare answers. After you make your presentation to the dissertation committee, they will likely pose some questions. Though you may not be able to predict every question that they could ask, you can predict some and prepare answers to better prepare for this section of the process.
Prepare a written proposal. Follow your school's proposal format when writing your dissertation proposal. Have this proposal prepared when you head in to give your presentation as you will likely be expected to give it to the committee at the conclusion of your presentation.