Keep these things in mind:
Animate a skeleton or silhouette before you add all the detail and such. This helps immensely.
The contact frame (where the foot is touching the ground, but no weight is yet on it) going into the recoil frame (where there full foot is on the ground, and the leg is bent with the full body weight landing on it) will give then run weight and make it look like she is actually hitting the ground.
The arms move like a pendulum, they do not move at a constant speed back and forth. They are moving fastest at the bottom of the arc.
The shoulders rotate with the arms, and the pelvis rotates opposite of the shoulders. There is a twisting motion in the torso, and without it you will get what looks like a paper doll running.
The entire body moved up and down as you run in a smooth sine wave. The top of the head does not stay level, and it does not jerk around. It moves smoothly up and down with the body.
I think if you just try and animate the girls silhouette (with different colors for each body part to differentiate), while referencing that image posted above me, you'll be able to finish this. Also, if you want an 8 frame run, then omit frames 1, 5, and 10. That will give you recoil, passing, high point, contact, recoil, passing, high point, contact.