Levels
Levels is a tool that lets you move the black point, white point and midtone of your photo under the histogram. You drag the sliders inward to where your image data begins, setting a solid contrast range in one go. It's a fast, precise way to stretch your tonal range.
Drag the black slider right to where the histogram starts, and the white one left to where it ends: that way you use the full range without wasting detail. The middle slider (gamma) brightens or darkens the photo without touching the black and white points. In Photoshop, use Levels as an adjustment layer to keep it non-destructive. For smoother transitions, reach for the tone curve afterward.
Read also the in-depth explanation: Levels explained.
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.