People have different approaches to this. Some will suggest starting off with the literature review, but personally, I find that to be inefficient, especially since you can be writing other sections in between reading the literature you need to review.
My preference has always been to start with a basic outline. Use the outline to determine what order will the chapters follow (this often is not the actual order the experiments were done in, but an order that makes for good logical flow from one idea to the next), what the main content of each chapter will be, bullet points of your major results and what you will discuss/conclude relative to those results.
Then, I write the methods. Knowing the order you're going to discuss things helps get that section organized quickly, and it's the easiest thing to write since you already know what methods you used. Once you have the methods, you can then write your results. After the methods and results are written and organized, follow the same structure for writing your discussion. After the methods, results and discussion is all written, then it's much easier to go back and write an introduction that properly sets up the chapter with the information needed to follow the discussion.
After all of the chapters are written, then it will be so much easier to write the overall lit review/thesis introduction. You'll have had to read all the literature to prepare the individual chapters, and now you can organize is logically to address what you finally decided to include in your thesis.
The more time you spend thinking about the organization and preparing a good outline before beginning, the less time you'll need to spend rearranging and rewriting chapters and sections.
Keep in active communication with your mentor during the writing process. Don't write everything and then hand them 300 pages to read all at once. Give them a chapter or section at a time to get feedback before you move on. Definitely discuss the outline with them before you start writing. This will save you a lot of time if what you have in mind is entirely different from how your mentor envisioned you should organize it.