Equinox80 You need to test them by watching if the movement matches up with how fast the character moves. You then adjust either movement speed or animation speed till you find one that looks/feels right. There isn't a predefined magic number for each game type. You need to experiment and watch. Factors that will affect it:
Sprite Size
Leg Movement Speed
Parallax Scrolling
Sprite Movement/Acceleration
If the character moves too fast and the legs don't move fast enough you will get a "moon walk" effect like Michael Jackson.
If the character moves slowly and the walk animation appears to quick, it will seem you are walking in quick sand, etc...
This part is really about trial and error :)