Any other tips for how to prepare for the interviews?
I don't think you need to do a whole lot of research about the judge's past opinions. I'd say only do this if you have an interest in the type of case and can comment on the subject matter. The judge's recent opinions will not come up unless you bring it up, and you should have good context for bringing up an old opinion. I researched the judges' opinions, read a few, but never brought them up in the interviews. All the judges made offers.
Do a little bit of research on the judge's bio to see if anything sparks your interest. This would be a basic start for the federal judge if the court website is not helpful: http://www.fjc.gov/public/home.nsf/hisj
My advice would be the same for any interview: be yourself, be calm, be positive, and prepare a few questions for both the judge and his/her clerks or staff attorneys. Take some time to think about what you like best about law school and the profession. Make sure you have a good answer for what you hope to accomplish with your law degree. Bring a copy of your resume and a list of professional references (if not already on your resume).
Remember: getting the interview is often the hardest part. You've already got your foot in the door - they like your credentials. Now you just have to make sure they like you, too. (And of course, make sure you like them, too!).