Understanding Lens Flare

Lens flare can appear as a general haze across the picture that lightens it reducing contrast. It can also appear as streaks across the picture or shapes, usually circles, in the picture.Flare is commonly associated with sunlight, but can occur as the result of any bright light in the area.

How to Avoid Lens Flare

Avoiding lens flare can be quite simple. Here are some easy tips.

Shield Your Lens from the Sun

You can shield your lens from the sun to make sure that the glare doesn't hit its glass elements. The easiest way to do this is with a lens hood. A lens hood is a cylindrical peice of plastic that screws onto the end of your lens. They can have a straight or tulip-style edges.
If you don't have a lens hood with you, you can improvise by shielding your lens with your hand or a piece of paper.

Use a Prime Lens

Prime lenses usually produce less flare then zoom lenses because they contain fewer glass elements. The more glass in your lens the more opportunities for light to bounce around inside it.
If you are using a zoom lens, you'll find that changing the focal length can reduce flare some. Try taking the picture at different focal lengths to see if you can minimize flare.

Watch Your Composition

Taking your picture in the direction of the a bright light like the sun will increase the occurrence of flare. Having the light in the picture or even just out of the frame can cause streaks and haze in your photo. Compose your picture so that the sun or other bright lights are well out of frame.

Using Lens Flare

Understanding lens flare is important to being able to use it artistically in your pictures. You don't have to always avoid it. It can add to your pictures too. Image editing programs like Photoshop even allow you to add flare to your pictures after you've taken them.
Here are some tips to help you add flare to your photos.

Aim at the Sun

Taking your photo in the direction of the sun will help you get flare. Just put your subject between you and the light.

Use Manual Mode

When taking pictures in the direction of the light use manual mode. On automatic your camera will tend to underexpose the image. It will expose for the light, but leave your subject as a silhouette in the frame.
You may have to take the picture using manual focus too. Sometimes your camera will be confused by the bright light shining in its direction and won't know what to focus on. (read article about : The Art of Manual setting mode  in SLR Photography).

Add it Later

Flare is easy enough to achieve, but if you decide after the fact that you wanted some flare in your picture you can always add it later in Photoshop.

Article from http://www.digital-photography-advisor.com