Star Trek

The way I did it was to watch it all from the beginning and go straight through. It took a little over a year, but I wasn't going at the most steady pace. For The Original Series, you can find lists of "the 30 good ones," or something like that. Then I'd watch the first six movies. Then straight through The Next Generation, then the next four movies. Then Deep Space Nine, Voyager, and Enterprise. I'm in the camp that the J.J.Abrams movies don't count, so watching those is up to you. After that, the new ones! Discovery, Picard, Lower Decks, Prodigy, Strange New Worlds. It's a long journey but well worth it.

Optionally, many many people are willing to give you sample episodes from each series as a starter point, then you can just jump around as you wish. The only ones you really need to watch fully in order are Deep Space Nine, and the new ones as they're pretty much all serialized, or have significant underlying continuity.