Do I pick apart published adventures and rework them?
Well, always when I use them. Basically, an adventure gets read as (i) a piece of prose telling a story, and (ii) as a selection of ideas for handling certain situations, character types, monsters, etc.
I find that part (i) is important: I need to get a feel for what kind of story this adventure produces. I tend to be something of a narrativist as a DM, so the ideas behind the story, and the way that the author imagines that it progresses are important to me. Plus, if I can get a firm grip on the story now, it makes any conversion and subsequent running much easier.
Part (ii) is the idea mine part. I don't expect that
my PCs will follow the same path, talk to the same people, or even care about the same things. So I am used to "winging it" according to their actions. If I have read through and written some notes about the author's expectations then I have something to fall back on when my own imagination draws a blank.
This brings me round to your question about NPCs being boring in play. Yes, I too tend to fall back on certain stereotypes in play. I tend not to have a single stereotype for a certain category, but a few tried and tested approaches. For example, my shop owners come in the (i) unctuous and keen to serve; (ii) extremely professional and rather judgemental; or (iii) shady and dubious varieties. Then again, since the PCs tend to interact with them only briefly, I don't think that they really care so long as they get what they want from him or her!
However, any stereotype can be grown as necessary, if the PCs interact with them more than expected. After all, they only probably dealt with them briefly, and they may not have seen the full range of their personality. I recall one somewhat mysterious if professional innkeeper that the PCs met, when they stayed at an inn that seemed too good to be true. Well, they actuualy liked the place, came back again and again and got to know the landlord well. Over time they uncovered that he was in fact a vampire, who ran an inn which provided custom to more unusual patrons: lycanthropes, plane-touched and certain undead. But he ran a very tight ship and brooked no trouble from any of his guests (as a male human vampire Sor12, that's not surprising really!), which meant it took the PCs a while to work it out.
Now, of course, I didn't know all this the first time they stayed at the
Dragon Ascendant inn. I just commented that the landlord was very pale and had a slightly odd accent. Everything else grew organically. That's the trick, I think, to successful NPCs. Just like people in real life, we discover more about someone the more we encounter them and interact with them. Don't be surprised if the person you talk to for all of 2 minutes, dealing only with business, seems a little bland. It has already been commented that that's just like real life. Just be prepared as DM to work more material in as the story progresses.
One other thing I do is keep my eyes open in real life for people who are different, or pique my interest for some reason. For example, recently I dealt with a newspaper seller who was physically rather unusual (short, very portly, with a retreating lower jaw, big teeth and a high, protruding forehead). He also spoke in a really earnest way, leaning foreward, when he felt he knew something, and mumbling when he wasn't so sure. This person, though he doesn't know it, became the Chief Librarian of the School of Wizardry. This guy bored the pants off the wizard PC, but he persevered in dealing with him and made a lifelong friend who gave him preferential access to the library's special texts. And everyone, even those who found him really annoying, also said he was really memorable.
NPCs take practise, and they can be quite a lot of work when they are key to the storyline. But this is a role-playing game, and persistence in this matter really pays off. Good luck with the DMing!
