So maybe you can share a little more about your AP?
Thanks, Quickleaf! Normally I'm all about a quasi-sand-box approach to gaming, but I'll be an engineering student for at least two more years. And well, I just don't have much time or energy for weekly game prep. And I pretty much suck at improving and winging things.
Let's see...what have I decided thus far? Well, my AP will take place in a fairly typical PoLand, though it includes a few quirks of my own. For example, it bugs me when really weird monsters like beholders and mind flayers are just...
there, wandering around an inexplicably huge network of subterranean passages. So instead of an underdark inhabited by randomly weird monsters, my setting has a sort of space-scape inhabited by very purposeful and organized aberrants.
And they have a plan.
(If you've played Diablo 2, think of the Arcane Sanctuary, except with creepy
them type monsters rather than ravening demons. And a similar origin story.)
My AP will involve all the usual foes -- demons, devils, selfish mortals, etc. -- but the aberrants are the masterminds. Their goal is total 'conversion' of the fading mortal world, and their strategy is to play the more numerous evil-types off of each other and mortals. So a lot of the AP will be about the PCs slaying devil cults, desperate humanoids, small demon hordes, dragons, and such, before they figure out who the real puppet master is.
Also, there will be a portal to Sigil somewhere nearby just because I'm still a PS fan.

Plus, it makes a convenient explanation if someone wants to play a weird race!
In addition, APs by their very nature, have a little bit of railroading that can turn off some people. I find, personally, that a lot of that can be avoided as long as you have buy in from you players on what kind of game you are playing. Trying to bring in "open world" free form players into something thats a little more scripted can cause problems. My point, I guess, is to keep in mind your audience and design the adventure accordingly. There is nothing wrong with an adventure designed for a group of religious warriors as long as the players know in advance and create their characters with that knowledge. Most AP's have really good player's guides that cover this.
Story and character continuity, got it. Good stuff!
As for railroading, well, I'll be an engineering student at a new school next September. So if I end up DMing this AP, I will have certainly gone through the "I'd love to DM, but I don't have the time or energy for anything other than an AP. So if not my AP, it's someone else running the game, or we go watch football..." conversation.* Not that I'll be forbidding minor side-tracks with an iron fist, but I'll be leaning on my players generally going along with the AP.
*No, that's a lie. I don't watch football.
