Some time ago, I wrote a post about how to construct the outline of your dissertation.
If you haven't read it: here's the summary of the idea. If you simply sit down one day and expect that you can start typing up your thesis from the first sentence of your introduction to the last sentence of your conclusions, you might need to reconsider your plan. Probably you could type up the whole thing from A to Z, but unless you have magnificent writing skills and an exceptional memory, you'll have a very hard time keeping the red thread through your text clear for the reader.
Therefore, my advice is to sit down with your research questions first, and sketch how you've gone about answering your research question. Then, you need to identify the logic that ties together the different subquestions of your research question that you answered. To have this relation visualized, I recommend that you make a simple scheme/diagram in whihc you show how the different chapters of your thesis are related.
One reader asked me the following question:
Great advice. An example of a diagram would have helped!
I didn't reply immediately, but I promised a post in which I could actually upload a drawing.
I'll write a follow-up post!
And here you can see the sketch that I used for my dissertation:
It's really quite simple - showing that I used both theory and experiments to tackle my research question, and from there developed a proposal to extend the existing design code and applied the insights of my research into case studies of existing bridges. In the very end, all previous chapters tie back together in the conclusions.
And while this diagram might look overly simple, it helped me tremendously to know what needs to go where in my dissertation, and which elements from every chapter are related to the next chapter(s).