The use of symmetry can be a powerful compositional technique, but it is difficult to offer definitive advice because symmetry can also ruin an image. A dominant point of interest helps a symmetrical composition, as can an appropriately used break in a symmetrical design. This tends to introduce tension or stress into an image so it is important that a break of symmetry is placed carefully. Left-right (horizontal) symmetry seems to work very well although top-bottom (vertical) symmetry and even diagonal symmetry can be used successfully.
Symmetry can be found almost anywhere in both man-made and natural environments. Sometimes it is just a matter of looking closer, or zooming in to some detail where unexpected symmetry exists. The technique can also be used even when mirror-like symmetry cannot be found. The shapes and contours of a secondary object can sometimes be used to balance those of the principal subject.