10 useful and not very known Photoshop tricks
1. Saving your .psd with all layers hidden makes a smaller file compared to saving it with all layers visible.
2. You can use the Crop Tool to quickly increase the canvas size of an image by holding down Ctrl + Alt whilst dragging the Crop Tool outside the current canvas.
3. If you want to see only one of your layers at a time, hold down Alt whilst clicking the eye icon of the layer. (do it again to show all layers again)
4. Holding down Alt while in a dialog box turns the Cancel button into a Reset button, so you can reset the values back to default.
5. If you want to just quickly check a very heavy .psd file, you can hold down Shift + Alt while clicking the Open button. This way Photoshop will open a flattened version of the file.
6. You can change the gray background that surrounds your image with the Paint Bucket Tool, just hold down Shift and make click on the background.
7. Not a very unknown tip, but if you hold down the space bar while using any tool, you'll quickly change to the Hand Tool. Aditionally, you can change to the Move Tool by holding down Ctrl. If you hold down Alt while using the Brush Tool you'll quickly change to the Eyedropper Tool. If you do it while using the Move Tool you'll duplicate the layer.
8. If you thought Photoshop only allowed you to perform one undo (Ctrl + Z), by using Ctrl + Alt + Z you can do more than one. Alternatively with Ctrl + Shift + Z you can perform a redo.
9. Ctrl. + Tab toggles between your current open documents.
10. Pressing X switches the background and foreground colors.