Inverting A Mask As You Move It
This isn’t a hard tip, but it’s the kind of thing that only advanced users would want to do. It’s the hidden shortcut for inverting a layer mask as you duplicate it (see what I mean)? Well, anyway, here’s the tip: First hold the Shift key, then click-and-drag the layer mask thumbnail to the layer you want it to appear on. If you want to invert and duplicate the mask (rather than move it), hold the Option key (PC: Alt key) as well—so the shortcut is Option-Shift (PC: Alt-Shift) to duplicate and invert.