Click on the about me & FAQ - Make sure you read through the FAQ. You don't want to ask someone a question that is already on that page. You want to give your readers this exclusive, interesting, inside look at the person.
Master the art of skimming - Skim some recent and some old blog posts. Is the tone different? Have they changed, or has their writing changed?
Think about your audience - Think about what your audience wants, what are their interests? Tweak your questions to interest them.
Have a database to fall back on - Not every single question is super customized and personal. Have a list of questions in your back pocket to pull out and fill in needed space.
Have fun with it - It depends on your platform and audience, but don't be afraid to ask fun questions. Ask them about their favorite cocktail or what they do to let loose. Don't make the interview too serious.