First, switch your camera to macro mode. Usually, this is shown by a tulip symbol - either on the camera's external controls or on its onscreen menu. Macro mode allows your camera to focus on objects just a few inches away. Turn it off afterwards or your normal photos will be blurred.
There's often a noticeable difference between the image seen through a camera's viewfinder and the image captured. The lens is situated in a different place to the viewfinder and the disparity can cause a ‘parallax error' (a subject centred using the viewfinder will be off-centre in the final picture).
Parallax errors are only a significant problem with macro shots. Being very close to your subject matter dramatically increases the distortion. If there are correction markings on your viewfinder, you should use them. To be absolutely sure of getting the correct composition, use the LCD to compose shots.
Another major difference between normal and macro photography is the depth of field. This describes the amount of your image that will be in focus, radiating outwards from your main focal point. With a macro shot, it can drop to as little as 1cm, meaning that a large portion of your picture may be blurred.
You can compensate a little if your camera has an Aperture Priority mode. This is represented by the letter A and will allow you to select a larger aperture value. If you can't select this mode, don't despair. As long as you get the main element in focus, the blurry background will add to the impact of the photograph.
Your camera's manual will tell you its closest focal distance in macro mode, but you can find out the perfect distance using a process of trial and error. Learning your camera's limits will help you to take quick shots - you won't waste time trying to focus on a subject you know is too far away or too close to your lens.