One of the basic things you need to know about digital cameras is the concept of shutter lag. What is shutter lag? Well, it's the time lag between the moment you depress the shutter button to the time the camera actually options the shutter to capture the shot. This lag is mostly inevitable, especially in older digital cameras - due to the limitations in mechanics between the shutter button and the camera optics.

Many budding photographers ignore this lag and expect that a photo will be captured the precise moment the shutter button is depressed. The result? Out of focus pictures and poor quality. It'll also lead to many missed photo opportunities and quite a bit of frustration.

The solution to the shutter lag problem is to learn to pre-focus. What does this mean? Well to pre-focus means to press down half-way on the shutter button while you compose the shot. Don't depress it fully yet.

Only when the shot is nicely composed and you've all your subjects smiling properly and so forth, do you fully depress the shutter button. By doing this, the camera will take the picture the moment you fully depress the button - leading to much less or negligible lag.

With pre-focus, you're better able to capture shots on demand
 

So train yourself to walk around with the camera's shutter button half depressed! I know I do it very often when I'm out for vacations and seeing many photo opportunities around me!

Most new digital cameras these days have mechanics which significantly reduce shutter lag. However, on older digital cameras have the lag issue and that's where you need to apply the pre-focus technique. Whenever I'm holding an old digital camera (e.g. I still have an old Canon Digital IXUS from five years ago) - I'm conscious I should always depress the shutter button halfway down, readying myself for any photo opportunity that comes up.