Here are some tips and tricks for using Photoshop:
Quickly select layers: With the Move tool selected, right-click in the image over the layer to be selected and choose it from the context-sensitive menu. Note: this shortcut works better if you name your layers.
Reposition selections while drawing: After starting to draw a selection using the Marquee tool, holding the spacebar (while still holding the mouse down) allows the repositioning of the origin of the selection. Releasing the spacebar (while still holding the mouse down) allows continuation of drawing of the selection. Similarly, when drawing with the Pen tool, if you click to set down an anchor point and need to reposition it, holding the spacebar allows you to reposition that anchor point – as long as you have not released the mouse after clicking to set the point.
Cycle through nested tools: To cycle through tools that use the same keyboard shortcut, add the Shift key. For example, Shift + L will cycle through the Lasso, Polygonal, and Magnetic Lasso Tools. If you prefer to cycle through tools that have the same shortcut without using the Shift key, choose Preferences > Tools and disable Use Shift Key for Tool Switch. To quickly cycle through nested tools without using a keyboard shortcut, Alt-click on the tool in the Toolbar. Or, learn how to create your own custom keyboard shortcut.
Toggling between tools: There are several tools which, with the help of a keyboard modifier, can be temporarily toggled to another tool. For example, to temporarily toggle between the Path Selection Tool and the Direct Selection Tool, hold the Control key. Other tools toggle with the help of the Alt key.Erase with history: Holding Alt key with the Eraser tool will erase with history.
Quickly fill or erase areas: The Paint Bucket can fill with the Foreground color or a Pattern (via the drop-down menu in the Options bar). Note: the Fill command (Edit > Fill) also has the pattern option, but the Paint Bucket may be faster than using the command.
The Ruler Tool: To rotate or straighten a layer (without affecting the entire document), click-drag using the Ruler tool then, click the Straighten Layer button in the Options bar.
Block mode: The Eraser tool has a special “Block” mode which gives you an eraser in the shape of a square.
Remember, these are just a few tips and tricks to help you get started with Photoshop. There are many more shortcuts and techniques to explore!