I agree with the others saying start with TNG season 1. Just know, some of the episodes are rough. They took a little while to find their feet. Check episode ratings on review sites, if you want to avoid the bad ones.

I’ve recently started getting a friend into Trek myself. They’re more into DS9, because they’ve been seeing memes about the Bell Riots, so we’ve been taking it slow on the other series. We decided to do a Best Of for TNG to begin with. So far, we watched episodes 1 and 2, Encounter at Farpoint, as well as episode 12, Datalore. Then we skipped straight to season 2, and watched episodes 3, 8, 9, 16, and 21. We also watched episode 16, Samaritan Snare, but only because it’s relevant to Star Trek: Lower Decks lol