A commonly used technique in photography is frames. This involves using objects to frame an image. The world is full of objects which make perfect natural frames, such as trees, archways and holes. By placing these around the edge of the composition you help to isolate the main subject from the outside world. The result is a more focussed image which draws your eye naturally to the main point of interest.
source: Les Bessant, flickr
Framing your shots - Digital Photography School
Images (where not attributed)