Kind of a stupid question, but what would be a good starting point for someone who has never really watched Star Trek?
The Den of Geek has guides on which episodes are essential to which series. To get into Star Trek, you also have to keep in mind what to expect.
- The Original Series from the 60s is very much a television adventure format. Little continuity, little storytelling, a lot of hippie ideals but a lot of whacko ideas. Very inconsistent quality of writing.
- Original cast movies are simple - watch the even numbered ones, skip the odd ones.
- The Next Generation is bright, optimistic, spandex-clad. Some brilliant episodes, but also some crap ones. Continuity and "canon" become a thing. A lot of trust in technology means that deep ethical dilemmas are often solved through technological hand-waving.
- TNG movies are simple - skip all except for First Contact
- DS9 moves both into serialized storytelling mode as well as looking at the darker side of the Star Trek universe - even in a utopia, there still is realpolitik, secret services and deep ethical dilemmas that can't be solved with the waving of a hand. My personal favorite.
- Voyager tries to move back to a TNG vibe, but mostly is a set of missed oppurtunities due to awful behind the scenes decisions. It seems like Rick Berman is an awful human being without any understanding of how TV and/or Star Trek works.
- ENT, the prequel series, is better than people give credit for. I'd rather not watch it first since it draws a lot of it's appeal from the viewer knowing what will come later.
- The same has to be said about Discovery, currently in it's third season, which is set between TNG's unaired first and second pilot. From my point of view it's the strongest Trek series since DS9, but it also profits massively from the viewer knowing about key Star Trek concepts and plot points.
- Finally Picard. I have not watched last night's season finale but so far I enjoyed it massively. It's moving TNG into a "premium streaming tv serial" world, and is surprisingly successful with it, while still not being TNG.