SLR cameras and some of the higher-end point-and-shoot cameras have filters that screw onto the front of their lenses. There are a wide variety of filters, and one of the most useful ones is the polarizing filter (such as those in this non-affiliate link).
Oftentimes, light will reflect off surfaces and create a glare. This often happens with bodies of water, and even in the sky on a hazy day. Polarizing filters only allow light to enter the camera from one direction, thus negating the off-angle incident light and giving more vibrancy to the scene.
In the image below, sunlight creates a glare by reflecting off the leaves on the branch. Using a polarizing filter, this glare is removed. This technique has often improved the images I've taken, whether portrait or landscape shots. Try one out yourself!
