The most important requirement is to get research results that can be written down in the dissertation. You may also find some recommendations in these discussions:

https://www.researchgate.net/post/Best_ways_for_PhD_proposal_and_PhD_Thesis/1

https://www.researchgate.net/post/What-are-the-ingredients-of-a-good-thesis/1

https://www.researchgate.net/post/How_to_structure_and_write_a_Good_PhD_Thesis/1

https://www.researchgate.net/post/What_are_the_best_research_practices_during_Ph_D_life/1

https://www.researchgate.net/post/Should_I_necessarily_limit_the_Scope_of_research/1

https://www.researchgate.net/post/I_have_just_started_my_doctoral_What_are_the_some_good_things_that_i_can_focus_on_apart_from_publications/1

Before writing your dissertation, it’s crucial to conduct thorough research to define your research question and objectives clearly. Review existing literature to identify gaps and ensure your topic is relevant and original. Create a detailed outline of your dissertation structure, including methodology, data collection methods, and timelines. Seek approval or feedback from your advisor on your research proposal. Additionally, ensure you have access to necessary resources, such as data, tools, or databases, and plan your time effectively to meet deadlines.

Before writing a dissertation, it is crucial to choose a well-defined, researchable topic that contributes to existing knowledge. Conducting a preliminary literature review helps identify key theories and research gaps. Clearly formulating research questions and objectives ensures focus and alignment with study goals. Selecting an appropriate methodology, whether qualitative, quantitative, or mixed-methods, is essential for data collection. Securing approval for the research proposal and obtaining ethical clearance (if required) ensures compliance with academic standards. Planning a realistic timeline helps in managing tasks effectively. Organizing data collection processes and testing tools enhances research accuracy. Structuring the dissertation with a clear outline aids in systematic writing. Reviewing formatting and citation guidelines prevents errors. These preparatory steps ensure a well-structured and high-quality dissertation.

I should say the following:

- thorough literature review on the topic of interest and then research gap identification

- conducting your experiments and hopefully obtaining results good enough to be included in the dissertation and hopefully published in a journal as well

- having a clear picture of what your thesis needs to look like and talking it out with your supervisor before starting to write

Why you should write your PhD thesis backwards

By considering the central statement of your entire PhD, you can structure your writing around it, says Tuuli Toivonen...

"Few things are as daunting as figuring out how — and where — to begin writing your PhD thesis. But considering the central statement of your entire research project can make structuring your writing much easier... Her recipe for a clear synopsis includes:

• Identifying your claims
• Structuring your introductory chapter around the claims
• Writing the introduction, background and data and methods sections last...

Writing the synopsis in this order could seem unorthodox in academia: you’re writing the middle and end first, and then filling out the rest later. But if your journey has been long and winding, with many articles to incorporate, starting with your central claim can help to crystallize your key insights.

At the very least, this approach ensures that when an emeritus professor fixes you with a sharp stare and asks, “What’s your claim?”, you’ll be confident in your answer. Perhaps the next time you’re writing a single journal article, you’ll find the approach useful there, too."

https://www.nature.com/articles/d41586-025-01061-8