To say your dissertation is qualitative is not specific enough. You need to identify the specific qualitative methodology at use in your dissertation. For example, is it a phenomenology, case study, grounded theory or something else? When you have this methodology identified, make sure you read as much as you can about the methodology. Consult books, research articles and conference presentations, and talk to experts in the field.
You need to carefully examine the literature related to your dissertation topic (and even research tangentially related to the topic) so you have a complete understanding of the research and theory behind your dissertation. Play close attention to any qualitative research on the topic and use it to ground your own methodology.
Another question you are likely to ask yourself and be asked by your committee is how you went about selecting participants for the study. There needs to be clear criteria for who became participants, particularly if any people were excluded. A qualitative study can have as little as one participant, such as a case study, and you will need to defend why the participants were the correct subjects about whom to gather data.
One of the most important research strategies for qualitative research is triangulation, or the process of using multiple sources of data to support a finding. For example, a finding based on data in interviews should be confirmed in observational data and field notes. When writing your qualitative dissertation, you will need to clearly indicate the pattern of triangulation for each finding.
It is a good idea to find other qualitative dissertations in your field of study. You can use them to help construct your own study and to help justify your qualitative design to your committee. Unless your field of study is very new, you are unlikely to have the first qualitative dissertation. Try to find dissertations with the same methodology as well.
The research questions of your qualitative dissertation are the heart of the study. These need to be carefully thought out and worded so that your committee knows exactly what you were researching. It is best to have your committee chair help you with the research questions. During the dissertation proposal defense, you may be asked to revise your questions.