Media Bistro offers tips. I like this one especially:
3. Don’t be flexible.
In college and high-school journalism, they tell you to be flexible in order to land an interview. Accommodate whatever they need (interview them in a cab, or even in the bathroom, if necessary) because they’re the VIPs and you need to work on their schedules. This sounds good, but it usually fails for me. When I give someone a big window of time, I find it stays open forever. Instead, say “I’d like to talk to you for 20 minutes next Wednesday or Thursday. Let’s do either 10 a.m., 1:00 p.m., or 2:00 p.m., Pacific time, either day.”