Almost
anyone is going to do a better job at telling you how to prep NPCs than me. But! All hope is not lost. I can still give you some techniques for shaping up your NPCs during the session itself.
I did an improv workshop over the weekend, and I fell mildly in love with the idea of "heightening" that they propose. Basically, they point out how powerful it is to have an actor heighten either (a) the amount of minor detail the audience knows, (b) the emotional relationships between people or (c) the stakes of a situation.
So here's my recommendation: When in doubt, with an NPC, take fifteen seconds, think of something in one of these categories, and throw it in. You never know what players will bite at. Here's how I'd do it:
Me: So the guard says "No. None may pass without written authorization."
Players: Oh, we should totally just
kill this guy, but I guess as paladins we can't. We try to convince him again.
Me: (think, think ... relationship!) He sees the amulet of your God. "Oh ... your grace! I did not realize! I ... I ... " he seems very torn. "I hesitate to bar the way of a man of God, but my orders ... what should I do, father? Do I follow my duty, or my faith?"
Players: Sheesh, Tony, always with the moral quandaries. I tell him "You must do what you think is best." Does he let us through?
Me: (think, think ... stakes!) He stands aside to let you through ... but just at that moment the castellan walks up, scowling. "Alric!" he snaps, "What manner of dereliction of duty is this!" Alric blanches.
Players: Oh for pete's sake. "The fault is mine ... I have been too insistent. And yet, it is important that I proceed!"
Me: (think, think ... detail!) The castellan glowers. "Alric, this is not like the time that you kept a cat at your post. You almost disobeyed your sworn lord!"
Players: Oh, that's
so cute! A castle guard with a little kitten tucked away in the back room? Man, we gotta take Alric with us. He rocks!
Me: (stupefied) Uh ... okay!Now the example I just gave is really pouring the heightening on. I expect it's better used as an occasional spice ... to taste, y'know? But examples are to exemplify, not for playing in