Having a clean or dramatic sky as a backdrop is an asset. Great sunsets, an alpenglow, an impending storm or one full of puffy white clouds all contribute to making better images. Shooting against a clear blue sky separates the subject from the background and emphasizes it. Psychologically, with the mind accustomed to seeing blue sky—whatever is offset against it, attracts the eye.
The ominous light from an impending storm is extremely moving. Whenever I encounter these magical moments, my main focus is finding a foreground subject to use as a center of interest. This type of light doesn’t last long so working quickly is a must. The same goes for the light of a sunrise or sunset as it reaches its climax.
Images made with the sky as a background can commonly be enhanced through the use of filters. For blue skies I’ll either use a polarizer to enrich the saturation of colors or a graduated neutral density to bring the exposure values of the sky closer to the value of the foreground elements. For sunrise/sunset shots I incorporate the use of a grad ND filter and/or an enhancing filter to bring out the most amount of color. At dawn and dusk, silhouettes with character and interesting form become key elements. Look for interesting shapes and include them into the composition. Vary both the focal length and vertical vs. horizontal orientation so you cover all possibilities and come back with the best image of the scene.