When photographing an object it is easy to aim the camera with the object dead center in the viewfinder and snap. Our main concern is on keeping the entire object within the borders of the viewfinder, getting good light and keeping our object in focus. The final thing needed to make the photo stand out is composition.
There is a technique used in photography, painting and most cases of design which is called the rule of third. This rule is based on the fact that when we look at something we tend to focus not on the dead center but slightly to the side of the far center. There is a natural urge in us to look for the final flaw which makes something unique.
To use the rule of third we can imagine two vertical and two horizontal lines over the scene we are about to photograph. While doing this we try to find a way of placing the main object in on of the four intersections, bringing in the rule of third into the composition. If the object itself can not be placed in the intersection, try to pick out a point in the object to focus on. If your object for example is a portrait of a person you can place one of the eyes in one of the intersections.
Remember though that the rule of third is not really a rule. It is a guideline which can be used to compose a better scene to photograph but there will always be photos which get even better by not go by the rules. An easy way to use the rule of third is to always ask if it can be applied for each photo taken. It can also be used but varied to match like in the instance of full body portraits. For these many photographers use more the shape of a cross where the body is centered horizontally and then placed so that the eye-line is located one third from the top. In a way a vertical variation of the rule of third.
Many new digital cameras today have an option to show guidelines in the viewfinder to make the composition easier. Please refer to you manual to find if your camera has this option or not.