A Smart Object base layer that has 2 Smart Filters, Sharpen + Shadow Highlight. Since this gives us a washed out, flat feel we will start by adjusting the contrast.
Today we will be using a Dodge and Burn layer.
To do this create a New Layer > Fill with 50% gray
With the gray layer selected go to your Layer Blending mode > change the mode to Overlay.
With the layer mode set to Overlay you will no longer see the gray over your image.
Now use the Brush Tool set it to Black or White with a 10% opacity. Select the Overlay layer and paint with the brush. Black will darken the area of the image you are painting over, White will brighten it.
As with all adjustments, universally go too far, then dial back the layer Opacity till you get a flattering effect.
Play with different brush hardness, opacity and size. To refine your brush's effect confine your brush to a selected area. This layer can also be effected by filters such as blur, sharpen, distort, etc.