You can copy items from multiple layers at a time in Photoshop by simply adding the Shift key to Command + C or selecting Copy from the Edit menu. Now when you paste, it will give you results as if you had flattened all your layers before making the copy command.
Many times you are stuck with a washed-out photo from digital camera or scanned photo. Most people who try, find that quick adjustments in Photoshop’s Levels or Curves dialogs will certainly boost the colors up, but they also destroy all the details in the photo. Fortunately, Photoshop offers layer modes! Make a duplicate of the photo on another layer, the easiest way is hitting Command + J. Then, set the layer mode of the newly created layer to Overlay. This should really boost the color & contrast, but not mess with your highlights and shadows.
Layer Sets in Photoshop are a great way to organize your layers but many times you will need to merge a set to work on its component layers as a merged, single layer. To do this, activate a layer set, go to the pop-out arrow in the upper right corner of the Layers palette, and drag down to Merge Layer Set. This will replace the set with a merged composite of the set’s component layers. But sometimes I want to get a merged version of a set to work with and maintain the set with its component layers intact. To do this, follow the same sequence above but hold down the Option key before you release over Merge Layer Set. This will merge the set out into a new layer above the existing layer set rather than replacing it.
Did you know that when you’re using a tool that has a Slider, such as the layer settings in the Layers Palette, after clicking the Slider button you can use the left and right arrow keys to increase or decrease the slider by 1%. You can also hold the Shift key down while pressing the arrow keys to increase or decrease the amount by 10% at a time. This is helpful when the area you’re adjusting is subtle and you want to keep your eye on the image, instead of the slider.
To select a color while in Photoshop from anywhere on the screen, simply select the Eyedropper tool, hold down the mouse key while you move around the screen until you’re over the color you want to grab – then just let go of the mouse button.