Before you press the shutter release button (take the picture) stop and look at what you can see through the view finder or what you can see on the screen on your camera.
Are there any distracting objects in view?
Are there any bright areas of the image that will distract the eye of the person looking at your image, away from the main point of focus?
Is everything in focus?
Could the picture be improved by moving a little?
Training yourself to stop and think for a few seconds can help you produce much more pleasing images.