You need to use cover, if any cover is provided. That means tightly sticking behind corners and visibly leaning to expose as little of your body to the targets as possible.
You need to remember not to do "speed reloads." Practice stowing a magazine in a pocket unless you are actually at slide lock, or you've had some malfunction.
Try to get a handle on "target priority." Targets you can see now have priority (and so must be engaged first) over targets you have to lean around obstacles to see. If you have several targets exposed to you from a position (or there's no cover) targets closest to you have priority over ones farther away. In USPSA, a smart shooter will often engage the farthest targets first and then pick up speed as he transitions through to the closest targets. Accelerating is easier than slowing down. In IDPA that would be exactly backwards. The targets closest to you are those most likely to KILL you -- engage them first.
If you're an accomplished USPSA gamer, listen closely to the stage description and do what you're told. There is much less flexibility in figuring out which targets to shoot from where, and in what order. There's a little, but not much. Do what the stage description says to do, in the order given.
Be very patient with these rules and try to get into the spirit of why they're there. If you (like some USPSA shooters) fixate on how they are in the way and slow you down and frustrate you, you might as well stop. If you start to get into why the rules are there, you'll find there are interesting challenges to IDPA that other sports don't present.