It may sound simple, but one of the simplest way to improve your photographs is by getting close to your subject. Unless you are intentionally trying to capture a wide angle view, move in close because that’s where the action is. The best way to get close is by physically moving closer to your subject. Zoom lens are great but they come at a cost. If you are using a digital SLR with a zoom lens, it probably has a variable maximum aperture setting. This means that zooming all the way in means you may need more light on the scene. For example a 35-135 mm zoom lens may have a variable aperture that goes from 3.5 at 35 mm to 5.6 at 135 mm. You will also need to be aware of camera shake when fully zoomed in. The more you zoom in, the more noticable your camera shake.
Why are my photos blurry?