Here are the shortcuts for the Adjustment Brush:
• Option (Mac) / Alt (Win) + “[“ or “]” increases/decreases brush size. Adding the Shift key increases/decreases feather (softness of the edge)
• 1-9 sets the Flow amount . Use 0 for 100%
• “A” toggles Auto Mask on/off.
• Option (Mac) / Alt (Win) toggles Adjustment Brush and Eraser tool.
• “/” (forward slash) toggles between brush A and B.
• Shift -drag constrains Adjustment Brush to a straight line.
• Tap Return to apply the brush and begin painting a new adjustment
• “O” Show/Hide Mask Overlay, Shift + O cycles Mask Overlay colors.
• “H” Hide/Show Pins.
And don’t forget, after choosing settings for a brush, you can save your new settings as a preset. To save a preset, at the top of the Adjustment Brush panel, click on the name of the currently selected preset (to the right of the word Effect) and choose Save Current Settings As New Preset form the drop down list.

can anyone explain the difference between the flow & density sliders?
The Flow sets the amount and speed at which an adjustment is applies , the Density caps the amount of change that can be made (even with multiple strokes). Try loading the brush with a huge adjustment (like +2 exposure) and then paint with different Flow and Density setting to see the difference.
Hi Julieanne,
Do you know how to drag a highly zoomed picture without leaving the actual brush mask?
Thanks!
Holding down the spacebar will temporarily give you the Hand too. Click-drag with the Hand tool to reposition the portion of the image that you want visible.