Animations Snap rather than blending well in blend trees

Hello,
I've never posted on one of these before but here goes. I've got a very good controller and animator but my humanoid mecanim does alot of snapping. When I go from idle to moving (or more obviously when I go from moving to idle) it snaps into the idle which is very obvious from the legs. I've tried slowing the controller input, and playing with the transition settings. My questions are:

1. How can I make it so that the legs smoothly move from the narrower gait position to the wider idle position?
2. What is the best method for determining the blend tree "threshold" values that should be used for a smooth transition?
3. What can I do with my animations to ensure seamless transitions between blend trees and between states? Should I be trying to plug in transition animations?

Any help is appreciated.