A "Sky" Photo seems the most popular for instagram users. Here are some of my favorite Sky Photos that I have taken. As you can see they are never just sky photos. I find plain images with no focal point less interesting. Which I suppose would be my first tip. The first Photo is of the Light Art Installation at the Los Angeles County Art Museum. The second is at the Huntington Library as seen through the large Glass Dome in the Courtyard.
These photos depict trees during a Sunset, which is a great time to take photos, I love the color change in the sky and depending on directing and time the sky varies in color!The Photo above shows the Sky in Blue and Purple Tones.
The Photo below shows the Sky in hues of Blue, Green and Yellow. The Trees also show how the Color of the Sky can be a greater focal point against Black Silhouettes.
The last Tip when it comes to Sky Photos that I use Clouds in different ways The Rose Bowl Photo has very light clouds in the background and although I wanted the Rose Bowl in the shot, the majority are of the clouds. The Second Photo I wanted the clouds to be in the corner instead of the majority of the shot that way they look light and soft against the dark boarder.
The last is a photo that uses to of my techniques: Clouds and Tree Silhouettes. As you can see I still left a corner for the viewer to see the sky and the lightness of the clouds.