A good interviewer knows what he wants to discover, and regardless of the job title those goals are pretty much the same. You'll notice that only one of these has anything to do with your ability to do the job - those skill sets, so critical in getting your foot in the door, are now the common ground between all the candidates.
Competency is the can-do part.
Itemize all your skills as they match the job's responsibilities, then recall an incident which shows that skill set in action. It's a given that you must be professionally competent, so don't hang your hopes of a job offer on just being able to do the work. There's more to it than that. The interviewer is looking for people who couple their abilities with a motivation to do a professional job, no matter what the circumstances of the day. Saying that you are a motivated guy won't really get the point across.