Wow, I had no idea that this was so complicated. I simply meter off my hand in the same light (adding a little exposure for my brownish wife or blackish pussycat), or just go w/ whatever the meter, in camera or in hand, says. It always looks good to me, and I'm fussy about this sort of thing. Maybe it's because I shoot Tri-X exclusively? It's pretty darned hard to screw up w/ that film. I do generally use a spot meter, but even w/ center weighted metering it always looks good. I never have any trouble nailing exposure w/ portraits.
For my purposes, using the right lens in the right light is the most important stuff. A soft side light from a window works great. I have to explain things to a new sitter, but I generally get a camera or meter right in the person's/cat's face, take a reading, lock exposure, back up, focus, and shoot. After that initial reading, fire away. But truthfully, unless there's just a lot of bad light (in which case I shouldn't be shooting a portrait anyway), just pick a distance, meter, and shoot. It's really about the right light. If I'm not exactly sure what look I'm after, bracket. And take LOTS of shots if it's important. You can never take too many shots when doing portraits, because you may never have that sitter in that light again.