Some useful Photoshop shortcuts:

Ctrl + O	Open
Ctrl + N	New File
Ctrl + S	Save
Ctrl + 0	Fit to Screen
Alt + Shift + Mouse Scroll	Zoom In/Out
Alt + Ctrl + 0	Display in Real Size
Ctrl + Z	Undo/Redo
Alt + Ctrl + Z	Step backward
Ctrl + Shift + Z	Step forward
Ctrl + Shift + N	New Layer
Ctrl + A	Select All
Ctrl + T	Free Transform (must be followed by hitting “Enter” to accept changes)
Ctrl + D	Deselect
Ctrl + Shift + I	Invert Selection
B	Brush Tool
]	Increase Brush Size
[	Decrease Brush Size
Ctrl + E	Merge Layers/Group
Ctrl + G	Group Layers
Ctrl + L	Levels
Ctrl + U	Hue and Saturation
Space Bar	Hold down to get the Hand Tool and move the screen