I've been messing with this for a while. I recently came across a youtube video I think is excellent (time will tell). My experience so far is aligned with what Ada Han says. I'm trying to work with her suggestions. I think it's a matter of time and practice.....
Here is the link to Ada's video:
https://www.youtube.com/watch?v=L6ro2R3esHA
Here is a different website that explains textually (with diagrams) what Ada is talking about:
http://lena.kiev.ua/voice/
Hope this helps....