In a previous post I mentioned the importance of using keyboard shortcuts. Here are some of my favorite little-known Photoshop keyboard shortcuts that are very useful:

Select next brush in brush picker= . (period)
Select previous brush in brush picker= , (comma)
Select first brush in brush picker=Shift-, (Shift-comma)
Last brush in brush picker= Shift . (Shift-period)

Activate Layer Mask= Command-\ (PC: Control-\)
Activate Layer= Command-2 (PC: Control-2)

Activate next layer down= Option-[ (PC: Alt-[)
Activate next layer up= Option-] (PC: Alt-])
Activate top layer= Option-. (PC: Alt-.)
Activate bottom layer= Option-, (PC: Alt-‘)

Move layer down the stack= Command-[ (PC: Control-[)
Move layer up the stack= Command-] (PC: Control-])
Move layer to the top of the stack= Command-Shift-] (PC: Control-Shift-])
Move layer to the bottom of the stack= Command-Shift-[ (PC: Control-Shift-[)

With the Move tool active, press 1-9 to change Layer Opacity from 10 – 90%
Press 0 to change Layer Opacity to 100%
Press 00 to change Layer Opacity to 0%

With the Move tool active, press Shift and 1-9 to change Layer Fill Opacity from 10 – 90%
Press Shift-0 to change Layer Fill Opacity to 100%
Press Shift-00 to change Layer Fill Opacity to 0%