How to Animate a Run Cycle

A run cycle has the same basic animation principles as a walk cycle - but with a lot more force.
Instead of just propelling our mass forward, we need to push it entirely off the ground.

These are the basic key frames for one step of a running cycle:

run cycle keyframes
Keyframes for a running cycle

This illustration shows only one step - remember to animate the second leg!

This is running at 14 frames per step (one leg), at 24 fps.

When animating a character walking from the front we need to show:

The body MASS going up and down
The legs bending in perspective
The feet flipping

Mass

Moves up and down as it does in the side view.
If you wish to elaborate - show the hips swinging - the foot that's forward brings its side of the pelvis down.

Drawing legs in perspective

Most of the foreshortening happens to calf.
The thigh gets fore-shortened as well but unless your character brings its knees up very high - don't shorten the thighs too much.

Flipping the Feet

If you are animating Flash or After Effects Cut Outs, you have no choice - You need to draw the foot from three angles and switch between them as you animate:

Frontal view, flat
Raised up, showing the laces
Flipped, showing the underside.

It's not very convincing otherwise.

Stylize the walk

For different kinds of characters, play with

Step Width - men take wide strides (gee, I wonder why!), women walk in narrow steps.
For a stylized feminine walk - cross the legs over, the way runway models walk. Swing the hips!
Most people point their feet outward. We don't walk all that straight!
Remember that regular people barely lift their feet off the ground - it's a waste of energy to lift the knees higher than needed.
Threre's no need to drag the feet, but for a natural looking walk, don't lift feet and knees more than is absolutely necessary.

Modify these simple key frames to fit your character.