When dragging a layer or selection near the edge of a document or layer, Photoshop snaps the edge of the object you’re working with to the edge of the document, layer, or selection that’s currently active. To prevent this, hold down the Control (PC: Ctrl) key after you start dragging the layer or selection and the snapping will be temporarily disabled.
Click-and-drag with the Rectangular Marquee tool (M) or Elliptical Marquee tool and then press-and-hold the Spacebar to reposition the selection before releasing the mouse button. This is especially useful when attempting to create an elliptical selection
that aligns with an existing object.
Cycle through blend modes
When the Move tool (V) is active, hold down the Shift key and press the plus (+) or minus (–) key to change the blend mode of the active layer in the Layers panel. If the Brush tool (B) or a retouching tool is active, then the same keyboard shortcut will change the
blend mode of the active tool instead in the Options Bar.
Fit on Screen
If you ever copy-and-paste an image from a larger image into a smaller one, and then proceed to transform (Command-T [PC: Ctrl-T]) the resulting layer, you’ll find that the transformation handles appear outside your view of the document (because they’re beyond the document’s bounds). When that’s the case, press Command- 0 (PC: Ctrl-0) to use the Fit on Screen command to see the transformation handles that are attached to the active layer.
Reset any tool
If any tool is acting oddly, consider resetting the tool. Right-click on the tool icon in the upper-left corner of the Options Bar and choose Reset Tool from the menu that appears.
Command-Z (PC: Ctrl-Z) works fine when all you want is to undo a single step. If you need to undo multiple steps, add the Option (PC: Alt) key to the aforementioned keyboard shortcut first to be able to apply multiple undos. You can also control how many undos are available. Choose Photoshop (PC: Edit)>Preferences> Performance and in the History & Cache section, change the History States setting.
Cycle through open windows
Press Control-Tab to cycle through the open documents in Photoshop. Adding the Shift key will reverse the direction that the documents are displayed in.
Brush to Eyedropper
Any time the Brush tool (B) is active, hold down the Option (PC: Alt) key and click on an open image to choose a color within the document to paint with. This is the same as temporarily switching to the Eyedropper tool (I).
Painting on a mask
When painting on a mask with the Brush tool (B), press X to swap the Foreground and Background colors, press D to reset the Foreground and Background colors to their defaults, and use the number keys on the keyboard to change the Opacity of the active brush in the Options Bar.
Target a layer
When the Move tool (V) is active, hold down the Command (PC: Ctrl) key and click to target the top-most layer that contains information that’s directly below your mouse position. Hold down the Shift key to add additional layers to the ones that are already selected.