Outline your research approach at the start of your thesis. State that you are going to combine both quantitative and qualitative research methods, then justify this approach. You could say that this has not been done before in your field, and you want to see how your method will affect results.
Alternatively you could argue that both qualitative and quantitative methods have weaknesses in different areas, and combining the two will provide a more well-rounded study. Defending your approach is vital in any thesis; you will lose marks if you do not do this.
Decide the exact methods you will use within the two methods. Will you be interviewing people, or focusing on statistics from larger groups? Furthermore, from what sources will you collect your information? Decide how your methods and sources will influence your study and your objectivity. Adapt your thesis and methods accordingly.
Choose which method will be used first. Traditionally, quantitative research is used in the later stages of a project, as it is more objective than qualitative research and also more rigid. Quantitative research is designed to use data already available and the researcher should have an idea of what he or she is looking for. Thus, you cannot use it until you have already collected quite a lot of data and really honed your ideas.
Use qualitative research in the early phases when you are unsure of what exactly you are looking for, or if you do not have any idea of what results you will find. Qualitative research is far more flexible and more subjective, as the data can be influenced more readily by the researcher's interpretation.
Break it down in the essay. Rather than jump from one form of analysis to another, try to compartmentalise the essay. For example, begin the essay with your qualitative results and your analysis. Continue with quantitative and again analyze both the data and the approach. Then combine the two in an overall analysis and discuss how and why results differ.