Program exposure mode is great, but not all of the time.
Use aperture-priority exposure mode, A or Av, when depth-of-field may be important.
Use a wide aperture, say f/4.0, when you want the background blurry.
Use a smaller aperture, say f/16, to make the background sharper.
Use shutter-priority exposure mode, S or Tv, when photographing motion.
Decide whether you want the motion to be frozen or a blur.
What shutter speed should you try if you want to blur motion?
1/8th of a second works well for many situations.
For more, go to the Camera Settings Flow Chart.
The next two sections discuss how viewfinders can be deceptive.