I strongly second the recommendation of On Writing, it is easily the most helpful book on the topic that I've ever read.
I don't think that I'd say that I do research--specifically market research, which is the kind of research you're talking about--as such. While I'm not tied in all that closely to the TTRPG scene, I have been playing these kinds of games for over twenty years, and I haven't been doing so blindfolded or covering my ears. I think I absorb a fair amount of information through what might best be described as osmosis about what PCs and GMs do not like in published adventures. Most of my ideas about tropes, including old tropes and how to play with or invert them, likewise just comes from a general immersion in creating and producing media.
It's worth stating I have never published an adventure for any edition of D&D, nor do I intend to if I understand the DMsGuild rates correctly (being, if I recall correctly, even more extortionate than selling products through Drive-Thru is), unless of course I can do so directly for WotC and get paid actual money to do it. I do not review the latest trends or tropes in adventure design before running homebrew adventures/campaigns for my players, and I never have. Instead I assign that mental bandwidth to catering to my players' preferences, wants, and needs, and the speciifcs of their characters' stories.