Back Lighting & Camera Settings
When shooting with a strong backlight you definitely want to use manual settings. A back light picture has to be significantly overexposed, otherwise the main subject will turn out completely dark and the background/sky correctly lit.
Therefore, select a wide aperture and experiment with the shutter speed to control the light. Try to take a few shots with auto settings just to get a sense of where to start experimenting. Mostly it varies from 1/100 to 1/800 seconds.
Another way of finding the right shutter speed is to measure the light with the spot metering. Here the camera will only measure a small area of the photograph – point at your subject and avoid underexposure.
Focusing the is one of the hardest parts of shooting a backlit subject. Cameras are definitely not very fond of shooting against the sun, you will often find that the autofocus does not work very well, or at all.
You might look in the viewfinder just to realize that you are completely blinded, and cannot see your subject by any chance. This is one of the most problematic parts of shooting with backlighting.
Try and keep your ISO as low as possible. There will be plenty of light to work with.
If you keep at it, you can achieve some great images that have a magical look about them.