I think at some point TOS is a needed watch, even after getting into TNG some. There's a lot of good stories and background there. But TNG is fine for a start, as it began assuming little to no knowledge of TOS from viewers then, trying to reboot the series. Like any series, the first season has some so-so episodes as they try to figure out the show and characters, but most aren't so bad as to say skip entirely, as usually there's some development that will be used later. TNG is a well rounded show, with DS9 and VOY being more nuanced plots that drive their story.

Discovery I wouldn't say avoid, but I never got pulled into it from various clips I've seen to care too much about it. Maybe because of the time travel stuff and how much they changed of "canon" things for me. Same issue I have with the Abrams movies, the casting was spot-on, terrible job and acting, but the stories... meh. And they touched the real canon that I live for with Star Trek, the ship. Way too much wrong with it. But the first scene from the 2009 movie, and the hook that gets Kirk to join Starfleet, yeah, that was pretty good writing, even if it broke earlier lore.

Star Trek TOS novel Kirk though... he's a legend. The good writers knew how to build depth to their characters, and none of the visual media, even Shatner, can touch book Kirk.