The first thing you need to do is learn how to focus your camera. There is more to focusing the camera than "half-clicking". Most SLRs have autofocus, but it's often not the most effective.

Experiment with different modes of auto-focus in your camera's options, such as "continuous auto focus". Each mode functions a little differently on each model, so figure out which one performs the best.

When you are not shooting action photography, try using manual focus.

Many people accidentally adjust the "Diapter" of their camera. That is the small switch above the viewfinder! It is for people that wear glasses!!!!

Also, when shooting things far away, you want to be "focusing to infinity". Position the focus ring on the far left to do so. In some lenses, you can "focus past infinity". DO NOT FOCUS PAST INFINITY unless you really know what you're doing.