A good research design is a foundational basis for good research. In that regard, the Research design model (see screenshot below) can be a helpful tool for conceptualizing your research:
From: Maxwell, Joseph A. 2005. Qualitative Research Design - An Interactive Approach. 2nd ed. Thousand Oaks, CA: Sage Publications.
When preparing for your Research proposal seminar, it might be a good idea to use this model to “draw” the research design for your overall PhD research. If applicable, it may be worthwhile to “draw” separate research designs for separate research studies - you could think of it as a nested structure of research designs.
While you should not get married too closely to your initial plans - it is about the planning rather than the plan itself - making your research design explicit can be a useful guide when conducting your research. For instance, if you do not know how what you do (methods) relates to what you want to understand (research questions), or if you go into your research without any (provisional) research question at all, you risk wasting time on collecting data you don’t need and writing papers that won’t get published.
As always, everybody’s TME PhD journey is individual. Some PhD students work within a pre-defined research project, with a more or less pre-defined research design. Some PhD students, however, have the freedom and responsibility to craft their research design more or less from the ground up.
As you read papers and collect data along your TME PhD journey, you will likely (hopefully) get inspired and develop a lot of interesting ideas for what you could do research on (and how). These ideas might be more or less concrete: from “I should do something with [theory A].” over “It would be really interesting to learn more about the relationship between [concept A] and [concept B].” to “I should write a paper about [topic A] together with [researcher B] from [perspective C]”. No matter how concrete your idea is: WRITE IT DOWN! This will be immensely helpful down the road and keep your research “pipeline” filled.