Mastering Photo ModesMost digital SLRs have different programming modes - one for portraits, one for fast action, another to set the shutter speed and have the camera select the proper aperture. Each mode has its own characteristics, and it's a good idea to learn what they are before assuming that you're really get what you want with one.
For example, I was trying to use one of the full programming modes once and learned the hard way that the camera automatically saved all the images in a JPEG format (a compressed image) rather than the RAW files (the image information as it comes off the sensor) I prefer. JPEGs are fine, except that to make the image smaller, software someone throws out data. That means it's harder to enlarge these images or do certain types of retouching or manipulation because you don't have available what the camera originally captured. A given mode can easily affect sharpness and color settings or make decisions that affect how the image will look at the end.
I"m not suggesting to only shoot manual mode, but read through the computer manual and see what decisions you may be making without realizing it.