When pressing the shutter release button, the camera will first determine exposure, set white balance and focus on your subject. Because of this, there will be a noticeable time lag before the actual picture is being taken. For moving subjects press the shutter a few moments before the decisive moment or you will miss the action. Some camera's are slower in this aspect than others.
Passive autofocus systems have trouble focusing if there is little or no contrast or the scene is too dark. When this happens, focus on another subject at the same distance or switch to manual focus. Horizontal lines in an image may pose problems which can be avoided by turning the camera on its side while focusing.
Active autofocus sends out an infrared signal which is reflected by the subject. Consequently when taking pictures through glass, autofocus will fail and manual focus needs to be selected.
When the subject is outside the focus area of the viewfinder, the camera will focus on the background and the subject will be unsharp. To avoid this, place the subject in the center of your viewfinder, hold the release button halfway and recompose your image before taking the picture. This is something to be aware of when photographing two people or objects that are placed to the sides of the image outisde the focus area.