This should be fairly obvious, but not everyone uses the network as much - or as well - as they could. As soon as you know the name of the person interviewing you (which most companies will tell you a few days in advance), the first thing you should do is look him or her up on LinkedIn.
Moving away from more formal methods, you can see which blogs your interviewer reads - and whether you share interests - by peeking at her LiveFyre and Disqus profiles. These two popular comment plug-ins allow readers to log in with a social network of their choice to comment on blog posts. Because all their comments are compiled together, you can see everything they've commented on. Brilliant, right?
For extra brownie points, comment on some (not all - that would be overkill) of the same posts your interviewer has commented on, both before and after the interview. If she sees your name out there in the wild, she might recognize it and be more likely to consider you for the job, especially if you comment on industry-relevant blogs.