Those aren't good examples of good art. You should imitate something much better. Otherwise, you'll follow in their wrong footsteps.
Follow your eyes. Where does it look? Does it focus extensively on one area? Does a certain feature pull your eyes toward it even though you want to look at other features? If it does, then that's a problem.
Ideally, the eye should be allowed to wander and casually wander back to the focal point. None of the examples do that. They all force the eyes to look at one spot. The last example is better than the others, but suffers the same problem.