For the best result of a nail polish application, which step should be performed after applying the base coat?

Applying two coats of polish color after the base coat is recommended for achieving the best nail polish application. The first coat provides an initial layer of color, while the second coat enhances the vibrancy and depth of that color. This layering technique helps to ensure that the polish appears even and smooth, minimizing any streaks or uneven spots that may occur with just one coat.

Additionally, applying a second coat increases the polish's longevity by providing more protection to the nail, making it less prone to chipping or fading. This method allows for better coverage, particularly when using lighter shades or sheer polishes, which often require multiple applications to achieve the desired opacity.

Other steps listed, such as applying just one coat of color or only a top coat after the base, do not achieve the same level of quality in polish application, as they fail to utilize the full potential of layering. Cleaning the nails with alcohol may be necessary at other points for sanitation or preparation but does not contribute directly to the enhancement of the color application itself.