@thebottomsupblog I have one daughter, 27, married and one (the elder, 29!) who has never dated. My 2 cents worth:
My husband and I always emphasised that the most important thing about getting to know someone (not just for dating purposes) was to have shared activities and values. This is harder when they have started work, so we encouraged school or church activities, volunteering etc. This way, you see the person when he’s not on his best behaviour or just focused on making a good impression on you. You get to see how he reacts when tired, disappointed, irritated, sick, etc. We also told them that how he treats other women is important - how does he treat his grandmother, mother, sister, maid etc? Is he considerate, polite? Because that’s how he will treat his girlfriend/wife when the initial romance wears off (which it will).
This all comes before any actual dating. Apps weren’t a thing when my kids were teens, so no experience with that. Physical attraction - we always told them that that wasn’t too important. Spark - not so important initially, though liking and shared interests (i.e. friendship) would be important. After all, your spouse should be your best friend. Someone who ghosts should be written off altogether.
As for boundaries, we were conservative. We said no single dating before 18 (and only after consulting us); group dates/activities until then. We instituted a “secret code”, just in case, though my girls never needed to use it, thankfully. This meaning that if they ever felt uncomfortable or in danger, they should call/message us the code, and we would pick them up or help extricate them. In general, I required them to tell me who they were going out with, where (at least in rough terms), etc., and until they were 18, curfew was 11pm. We were more flexible if we trusted the friends they were with, they had a safe way to get home or we were picking them up.
My girls never minded (not much, anyway) the rules and advice - they knew we were concerned for their wellbeing. My daughter is the 3rd generation who met her husband in university/church. I know that doesn’t work for everyone (I have another unmarried daughter), but it is a good way to start.