Finding Voice and avoiding distractions

One of the hardest things for me when starting a new book is finding the voice of that book. It's hard to shake off the one you've so deeply been immersed in, and start all over again. Most story ideas come to me as situations or settings, so I have to sort of write or feel my way into who the characters are. Which maybe isn't the best way to go about it. I suspect voice is something I need to develop more. What do you do to tap into the heart of your new character and get them to speak to you?

Then there's the distraction problem. I could set this story in modern day! In a fantasy world! In a parallel universe! In the Revolutionary War! In Malta! (Well--not really Malta. I know nothing about Malta except that I tend to like a lot of their Eurovision entries.) Since I could see fitting the plot into so many different settings (each with their own perks), it's hard not to get derailed. Once I'm 30k into the story I'm good, but despite this starting out as a (failed) NaNo novel, I'm essentially starting from scratch. I know I can write a complete novel because I've done it twice already, but it's certainly hard to stand at the bare beginnings all over again.