I'm not asking how to use the Vampire Lord's powers, but something more basic: how do you determine that it is time to switch to Vampire Lord form?

I've played around with the werewolf side of things a bit. It irked me that I was more powerful in my normal human form than in beast form, so I eventually made a melee character who didn't use armor. He could handle 1 or 2 enemies at a time, but more than that and it was time for him to turn into his werewolf form.

That worked out pretty well - the problem is, for a vampire build, most people seem to recommend a mage/stealth kind of character, and those types of builds turn out so powerful that it seems Vampire Lord form wouldn't give you any real advantages. I mean, I'm sure it's fun to float around and lob drain health at people, but why bother when you can stab some necks or use Illusion/Conjuration to defeat your enemies just as easily, if not more so?

Just curious how you set up your characters to get the best use out of the Vampire Lord stuff.

It all depends on your playstyle. If you are a mage then the vampiric grip and summoning would be your ideal choice. You are extremely effective with your powers so long as Serana isn't there. Vampire Lords take out groups with their drain health ball, the bat cloak hurts close opponents, etc so I'd say they'd be good for groups at a distance, they are adequate at melee for individuals.