I’ve kept this post here for memory’s sake, This post from 2009 ^^
We all use Photoshop daily, but after reading these tips, you might discover some things that were previously unknown to you. These tips will make the tasks you regularly perform easier and faster…
1- Use the Spacebar to Move Selections
You can move the selection without altering its shape or size by pressing the Spacebar while dragging the selection.
2- Increase Font Preview Size
To increase the font preview size, go to Edit > Preferences > General > Type and adjust the font preview size.
3- Adjust Values with the Mouse
To easily adjust values in Photoshop, simply click and drag to the right or left on the value field.
4- Quickly Zoom Out
To quickly zoom out, double-click the left mouse button on the magnifying glass icon in the toolbar.
5- Show Multiple Hidden Layers Together
To reveal multiple hidden layers at once, click and hold on the eye icon next to one layer and drag upward over the other eye icons to reveal them.
6- Hide All Layers Except the Selected One
If you want to view only one layer and hide all others, press Alt while clicking the eye icon next to the selected layer.
7- Select the Path of a Layer
To select the path of a specific layer, hold down Ctrl and click on the layer’s thumbnail in the Layers panel.
8- Quickly Change Blending Mode
To quickly change the blending mode of a layer, use Alt + Shift and press the - and + keys to cycle through the different modes.
9- Show Only the Work Area and Hide Tools and Panels
Press Tab to switch to this mode, which hides all tools and panels, leaving only the work area visible. Press Tab again to return to the default view.
10- Full-Screen Work Area
Press F to toggle between two full-screen modes and the normal view. The third press returns you to the standard view.