Sometimes images can gain a dramatic effect adding sunrays.
First, I selected a sky that had potential and increased the canvas size to accommodate the foreground. I then found a landscape image that was taken at sunset but lacked a pretty sky. In that image I selected the sky with the magic wand, then the inverse and used the move tool to drag the foreground into the composite. I cleaned the horizon using a 5-15 pixel eraser at about 80% hardness. You will note in the finished image that the sky was extended in the lower left corner simply by using the rubber stamp and then the burn tool to darken the horizon.
In Photoshop there are hundreds of ways to do most everything. I like to keep it simple whenever I can. In this example I duplicated the original sky to create a new layer, then used the polygon lasso to define a ray, with each emanating from a vanishing point. I feathered my selection 20 pixels, then in adjustments increased the brightness +10 to +20 and also made slight adjustments in contrast. Note that my selections include some dark areas, which represent shadows cast by obstructing clouds. These variations add realism, but take extra time. The process is similar except brightness is –10 to –20.
The biggest advantage of compositing is that each element can be adjusted individually. For instance, if the sky is grainy, a Gaussian blur can be added while still sharpening the foreground. The same holds true with saturation, contrast, and multiple other adjustments used to enhance the image. I then added a frame and my copyright and signature.