• For photos which have distracting lens distortion, I use the excellent PTLens.
• Levels > Options. I usually try one of the auto color corection algorithms at a clip something like [.5, .05].
• Then I make general Levels adjustment in RGB.
• Resize
• View actual pixels
• Hue/Saturation (manual, usually no change)
• Brightness/Contrast (manual, usually no change)
• Convert to Lab Color mode
• Select "Lightness" channel, view all channels
• Unsharp mask in Lightness channel (defaults [85%, 0.3, 1], manual adjust)
• Convert to RGB