Effects: Rule of thirds

There are points in the photo that are called power points. They tend to attract eye first. Placing subject as per the rule of third is visually pleasing. It is also probably that putting subject at 1/3rd gives equal importance to subject and surrounding. Read more about it here, http://en.wikipedia.org/wiki/Rule_of_thirds

Some of the photographers also use a triangle rule. choose any three of the power points and lay your subject that such that it forms a triangle with these three points ... and see the effect.