Once you've plotted a point on a curve in the Curves dialog (Command-M [PC: Control-M]), you can adjust these points by clicking-and-dragging them, but many ...
When you apply sharpening to your image using the Unsharp Mask filter (under Filter, choose Sharpen), make certain that when you apply it, you're viewing ...
When correcting images in Curves, Levels, etc., it's best to try to do all your corrections at one time rather than changing each setting individually ...