Pace yourself. Some people are successful with a mindset of pounding out a certain number of words or pages a day, but for others that just leaves them feeling like failures when they don't hit the mark. Find your pace, and allow yourself the right to modify it at any time. Writing is like any other endeavor - the more you do it, the better you get at it.
Assuming this isn't limited to those who are presently alive, I'd want a fun and prolific writer like Nora Ephron so I could pick her brain. And then, because I'm so interested in ancient history, I'd pick one of the Egyptian pharoahs (maybe Tut, or Ramses II). I better pick someone who's actually alive today - so that would be Tom Hanks, who, I think, would also enjoy the company of my other guests.
I've kind of already achieved that by being a published author, but I always thought it would be really cool to see a story I've written up on the big screen. I'm getting close to achieving that too because my mystery/thriller has been adapted as a ten-episode series and is currently being shopped, by a producer, to the streaming networks. Fingers crossed.