Try Enhance→Auto Contrast. If that doesn’t work well, undo it with Ctrl+Z (Command+Z on the Mac) and choose Enhance→Adjust Lighting→Shadows/Highlights or Levels.
Make sure that you have good tones in the shadows (dark areas), midtones (middle-toned areas), and highlights (light areas). Also ensure that you can see details in all the tonal ranges, as shown in the figure.