Before you begin writing your thesis, find out exactly what your program expects. Even if you have been publishing research as you go along, your thesis must be more than the sum of your publications.
Supervisory Committee: Hold a meeting of your supervisory committee and present your research and thesis ideas to them. The committee and your supervisor will determine whether or not you have enough data for a complete thesis. You don't want to find out after you have written the thesis that your supervisory committee feels you should conduct a bit more research.
Revisions to Outline: Before starting to write your thesis, create a detailed outline and discuss this with your supervisor and committee members to get their feedback and suggested revisions. They may have valuable insights into how to organize the content of the thesis, what data to include and potential areas that you should learn more about in preparation for your thesis defense.
Please refer to Dissertation and Thesis Preparation for information on preparing and formatting your thesis. If you follow these guidelines from the start, you will save yourself a lot of time later when polishing the final version of your thesis. Pay particular attention to the section Thesis Basics, as this information is very important for planning and preparing your thesis.