Photography is an art, and with every art there is complete freedom of expression. With that said, unless there is specific artistic intent behind them, there are a few common mistakes that will ruin a photo. Issues with lighting, white balance, composition, or contrast will result in a disappointing photograph if not mitigated.
Lighting in photography is complicated; too much or too little and the picture will be ruined. Having adequate ambient light to take a photograph is important. Even when there is plenty of ambient light, ensure that the subject is independently lit. Using the flash is the easiest way and will make the subject stand out against the background.
Too much light will ruin a photograph as surely as not enough. To compensate for washed-out pictures, adjust the camera's metering. The other option for fixing this is to adjust exposure compensation.
Too little light produces an indistinct and shadowy photo. There are a number of ways to compensate for too little light, but the easiest is to use flash. Flash will brighten the subject and make it stand out against the rest of the picture.
More information about light issues and mitigating them can be found here.
Even with the right light, the wrong white balance will make a picture look wrong. Every type of light source changes the appearance of colors. This is because light sources are not a pure white, but have different white balances. When a camera collects the light information from a picture, it tries to adjust for the current lighting but is fallible. The easiest way to check is to take a picture of a white/grey/black card that is certified to be a specific color, and compare the picture to the color of the card. If the shades are not perfectly lined up, adjust the white balance on the camera until they are the same.
A common mistake in photos is poor composition. There are many rules regarding composition, but the following are the essentials for a well-composed photograph:
Use the "rule of thirds" when placing a subject
Minimize blank space
Focus the camera on the subject
Keep the camera level
Getting the right contrast in a picture makes the details pop out and distinctly shows the subject against the background. Over- and under-exposed photographs will have indistinct detail and poor color capture, and everything blends together.
Using the built-in exposure compensation feature on the camera is the first step toward improving the contrast of a picture. Before making any other adjustments, the exposure needs to be gotten as close to ideal as possible.
To even the contrast of a dark subject against a bright background, use the flash. The light from the flash will even out the shadows and give distinct lighting to the subject.
Capturing a high-quality picture is an easy task, but there are a number of common mistakes that can turn a beautiful moment into a low-quality picture. Light, white balance, composition, or contrast issues will ruin a picture every time. These things are, fortunately, easy to mitigate with just a couple of adjustments.