Once you have a proper structure and guideline, you can now start describing your work as ideas occur to you, Note that you will probably find different ideas for different chapters as you go about doing more research, but it is crucial all the same to note down these points. If you ignore them you will forget and probably never get a chance to locate where you first found the references and points in the first place.
Review your chapter headings and start writing sub-headings to include. Note that you can only handle this step if you have already done enough research and prepared your data even if as a rough draft.
That said; go through all the chapters and titles you jotted done in the first stage and identify areas where you will need to include important sub-topics and graphical data. Write off headings you find unnecessary and then prepare to structure your work in a more professional way.
Although different elements of the paper demand different amount of attention, it is important to strike a balance in the different sections of your work. In addition, begin to check for coherence in your arguments, logic and a proper flow in your writing. You can also ask for feedback from colleagues and professionals while at this level in your dissertation. It is actually necessary to ask for feedback from your supervisor and other professionals even before you complete your project. Sometimes your work could have errors that can lower the quality of your final work. And only when others identify such mistakes can you fix them.
One reason why you need to ask for feedback from professionals is so that you can identify mistakes and correct them as early as possible. In that same spirit, visualize your word count limits early and edit upwards or downwards as you go along with the project. Look carefully for points that are no clear enough and argue them out well. In the end, you want a solid paper, with clear arguments and links that show the quality of the overall paper.