I've had my students do quite a bit of writing and from their work, I have gotten a clearer feel for voice. There is one student named Elisabeth who is so funny but she doesn't even mean to be funny. I told her how naturally funny she is and asked if she meant to be. She answered no. I'm a little worried that it might have been the tiniest of insults.
A few postulations about voice: Be yourself! But what if your protagonist is a 12 year old? The beauty of being old! Some of us more than others...we've been every YA/MG age. We know what it's like. Is all you need to do is look back to your youth.