References

Introduction to Maya Animation Walk Cycle 

This tutorial teaches how to create walk cycle in Autodesk Maya. At once I used it as a mode to learn about Maya again.
So that is some notes I sum up from the tutorial:

• Write MEL script to keyframe attributes that you want to in Channel box. That is very helpful to avoid unneeded keys. I could not understand how to write it, just using it as a available tool.
• Graph editor: 
• Get the idea of the movement line,  control keyframe without touching model, fix or delete unneeded keys.
• Give the movement nice and smooth by adjust handles.
• Set up the following through acts by using graph editor...
• Order of keyframe a walk cycle:
• Start from the bottom of body: center gravity -> hip -> feet 
• Upper body: notice of following acts.

 Here are my practice of walk cycle:

Richard Williams Run cycle

Richard Williams' The Animator's Survival Kit is a great book for animator. I have not have opportunity to read it carefully and doing all the practice follow this book, so this time I can focus on Run cycle that is one of the fundamental skill for animator. 

Preston Blair's Walk Cycles