.
The following key commands do not require clicking on the mask.

X                                               reverses Foreground and Background colors
Numbers                               number keys change the Opacity of a brush
[ and ]                                     makes a brush smaller and  larger
Shift [ and Shift ]               makes a brush softer and  harder
Opt Delete                             fills a mask with the Foreground color
Command I                           inverts a mask

The following key commands require clicking on the mask.

Control Click                        displays mask options
Opt Click                                 displays a mask in black and white
Shift Opt Click                      displays a mask as a red overlay

Command Click                   loads the mask as a selection
Shift Command Click        adds the mask to a selection
Option Command Click    subtracts the mask from a selection
Shift Option Command     loads the intersection of two masks
Shift Command I                  inverses a selection

Drag & drop                           to move a mask from one layer to another
Option drag & drop            to copy a mask from one layer to another

Read more about Selections & Masks.
Learn more in my digital photography and digital printing workshops.