How often should you wash you face in order to have perfect skin?

Depends. Determining the appropriate frequency to wash your face depends on many factors, like: 1) the type of skin you have -- is it dry? Oily? Sensitive?; 2) what you use to wash your face; 3) the presence of any underlying skin conditions. As such, there is no universal answer for everyone. A dermatologist can help you determine the right frequency and products to use, in individualizing a regimen.
In general. In general you can wash your face twice a day. Use a gentle facial cleanser and avoid harsh scrubs.