I've been a frequent DM in Dungeons and Dragons since shortly before the release of version 3 (I started very young). I don't have any experience with the Iron Kingdoms setting, so I can't help you there. I usually create my own worlds so that I have as much freedom as possible.
My best advice is probably to be prepared, but don't count too heavily on being ready for every contingency. You won't be able to predict everything your players might want to do, and the only alternative is to force them to only do things which you are prepared for. Which isn't good, obviously. I generally work fairly heavily off of improvisation, although I don't know how well that would work with a pre-written module.
A couple of other things that come to mind are the mood and atmosphere of the game. This is mostly subjective based off of the players involved, but it's very important (in my opinion) to the game. Some players like the game to be all about the fighting and dungeon-crawling, some like it to be more role-playing then fighting and some like it in between. Likewise, some players like the game more serious and some less. As I said, this is mostly subjective.
The bottom line, however, is to do whatever works for you. I've known a lot of DMs, and they have a lot of differing styles. My sister, for instance, prefers to have a very detailed plan and simply run everything straight from it. I've also been in some games where the DM basically made up everything as he went along (with varying degrees of success). As long as the game is enjoyable for you and your players, then you're doing a good job.