This week's 7-minute video shows you how to isolate the highlights and shadows from one image and blend them with those of another. It's quick, easy, and effective.
Much can be said of masking. Masking is the art of using the image to select itself. Masking lets you apply the entire weight of Photoshop to the task of editing a selection. And masking, thy name is alpha channel.
Every app offers a gradient tool. But Photoshop's is special. Not only can you paint a soft transition from black to white. But you can soften the transition from one image to another. It fades, swipes, and more.
If you use the magic wand tool, stop what you're doing and switch to Color Range. This outrageously useful command lets you select an image as easily as the wand. But with more flexibility and much better results.