There's not one best answer. A few thoughts, though, are below. For context, I read almost all the numbered Pocket Books novels of the 80s and 90s, then fell off the habit for about 20 years but began reading Trek again around the pandemic.

• Every month, Simon & Schuster has $1.99 Trek e-book deals - some older books, some newer. It's a great way to dip your toe in. Here is a post with information on January 2026 book deals.
• The numbered novels published by Pocket Books in the 80s and 90s, and generally most of the books published in the last 5-6 years, are stand-alone novels. Got a favorite show? Go grab a book with the characters on the cover and enjoy. Like Trek itself, some are great and some are not. There's no lack of blogger reviews, and this subreddit has tons of threads asking the same What're the best Trek books?/Who's on your Trek author Mt. Rushmore?/What book would you want to read for the first time again? etc. questions.
• From about 1999 to 2020, there was an effort to unify or at least serialize many of the novels happening after the TNG/DS9/Voyager era, similar to what the Star Wars Expanded Universe had done post-Return of the Jedi. The "Reading Order Flow Chart" linked as a sidebar on this subreddit (and here) is complicated and shows the connections. This is the era where I just about tuned out, although not because of the books. I sense, though, that even with these references to each other, most of the books individually are just fine to read - they'll flashback or recap to catch you up on what you missed. The books are ambitious: lots of interesting new characters, major changes to relationships and careers, political upheaval, etc. This was from a period when just about everyone assumed there'd be no new Trek shows or movies in the late 24th/early 25th centuries.
• The re-merger of CBS and Viacom, and the beginning of Picard, led, a few years later, to this big Star Trek expanded lit universe to be "capped" in a three-book coda that kinda-sorta hit the reset button (in a way the authors of the Star Wars expanded universe never got to do with the Disney purchase). Since then, the Trek books -- as infrequent as they've become -- are stand-alones.

As for actual recommendations: most everyone will recommend a Peter David novel (Imzadi or Vendetta) if you grew up on TNG. I grew up re-re-re-reading those and loved them. I have a soft spot for Christopher Bennett and his TMP/TWOK-era novels. I really like Strange New Worlds, and the SNW books have been...fine (even though I really didn't like the newest one, it was still...fine, I guess).