Using your camera's built in flash effectively, to get better looking photographs is a subject that is often overlooked.
Leaving your camera in an automatic mode is often convienent,
however there are times when your camera is fooled into thinking there
is enough light in the subject field and automatic just wont do. 
If time permits, and the photo is particularly important I recommend using your flash on every shot.  Not so much on scenic shots in daylight, but mostly for snapshots of people.  By putting your camera's flash in the fill flash mode, it will give you more vibrant colors and better skin tones of subjects all the time.