Animated Walk Cycle

The walk cycle is one of the most important learning concepts in animation--and also one of the most technically difficult, because it requires so much attention to the movement of opposing limbs.

However difficult, though, if you can learn to master a walk cycle then you can animate just about anything. There are many types of walk cycles, and you can vary the motion to match your character or his/her mood; you can do bouncy walks, shuffling walks, casual slouches. But the first and simplest is the standard upright walk, viewed from the side--and that's what we're going to attack in simplified form today.

You can cover the cycle of a full stride in 8 frames.

Here is a walking cycle Flash Tutorial.
Walking Cycle Tutorial
100 days of walk cycles
Here is a tutorial that criticizes the "Walking Cycle":
April Peter, Animator 
She has a good argument why the walking cycle is not the best way to learn.

Never stop thinking about who your character is.

 Each walk should be different to suite the weight, gait, strength, body type and attitude of the character. 

After you've finished the basic structure, you don't have to keep the keys of all the transformations on the same frames. Each separate rotation or translation can have a different timing.

Don't obsess about ending up with identical graphs for each step. Achieving perfect mathematics and achieving a good animation usually aren't the same thing.

In fact, try to dirty the walk up. For example, place the feet in a slightly different place every time. Play with the rotations of the torso, head or arms.