Social is a big part of the picture. Forget about posing for a moment; there's only so much that can wrong there unless you're trying something very much out of the ordinary.
What you may have failed to notice in all of that subtle direction you were following is that direction was only a small part of what was going on. You need to appear confident yourself (and if you're not actually confident, work on faking it). Most people would rather be in a dentist's chair than in front of a camera, and if looks like you don't quite know what you're doing (they're not looking at the technical, but reading you for uncertainty), then they'd probably rather be in a bad dentist's chair (at least he/she graduated dental college). The "photography" should be a done deal — even if you have to make adjustments (to the angle or distance of a light, changing framing, etc.) you should look like you know what you're adjusting and be able to explain why.
Then you have a choice: be a "people person" or learn how to fake it convincingly. If you want a happy subject, you'd better be a happy photographer. Engage in banter. If you can get them really smiling (not the "say cheese" smile) or laughing, the job's in the can. You can start with a little bit of the ol' "chin this way" stuff and taking pictures before they're ready to rock, but that's more to put them at ease and check you lighting/exposure than to get pictures at first. Make them comfortable, and once they're comfortable, there's not a lot to the rest of the shoot.
You may not have anything like the session time of, say, a Peter Hurley to work with, but you could do an awful lot worse than to watch his videos. There are a couple of longish segments from The Art Behind the Head Shot on YouTube that are free to watch. If you're looking to make a buck at portraiture or head shots, you just might find it to be worth your while to drop $300 on the full four-hour video set. (I reviewed it, and it's worth more to a beginning portraitist than a fast "portrait" lens or another flash would be.)
As for "posing", apart from reminding the subject to keep their head forward (to tighten up a double chin), there are no real rules. Everybody's a bit different, and you want the pose to match the rest of the look (unless deliberate incongruity is your thing). Feel it out and make it happen. Going for the rules-based cookie cutter approach is the best way to get shopping mall pictures. Get in touch with the subject, follow them where they're going, and when they're heading for something promising, help them along the journey. But it all starts with making a connection, with breaking the ice. You can be the greatest photographic technician the world has ever known, but if you can't be a "people person" on demand, then portraiture is probably not your game. (Fashion and beauty are different; a lot of the time you're looking for something a little aloof and unattainable, and an Aspy-type tech can usually handle that just fine.)
