I'm by no means an expert, but here are some tips I've picked up over the past year or so:
Prep
The Interview
Some other Resources
Longer-Term, the Turnaround is a podcast about interviewers and their techniques.
The chapter about interviews in Zinsser's On Writing Well was helpful for me. If you are pressed for time grab it at your library and just read that chapter, it's short. Amazon Link
> Get people talking. Learn to ask questions that will elicit answers about what is most interesting or vivid in their lives. Nothing so animates writing as someone telling what he thinks or what he does -- in his own words.
Zinsser, On Writing Well