Only Shades of Gray
A simple tip to creating believable retro imagery is never to use 100% black or white tones in the artwork. The retro look often relies on distressed or faded artifacts, and a foundation of grays in a subtle tonal spectrum can enhance the vintage believability. Unlike using Desaturate (Image>Adjustments>Desaturate), Image>Adjustments>Black & White gives you control over specific color values, tinting, hue and saturation as well as some presets with which to experiment.