You have to understand what your camera is trying to do when it determines a "proper" exposure. It is trying to set the exposure based on the assumption that the entire scene can be reduced to an 18% average grey. If you shoot a very bright scene, the camera will try to under expose (darken) to bring it back to the 18% grey. If you shoot a very dark scene, the camera will try to over expose (brighten) it to get it back to the 18% grey. Snowscapes, white flowers, bridal dresses, etc,... can look dark or muddy as a result. The point is that your camera's meter will not always get the correct exposure. This is where you have to step in and adjust the exposure based on what you are seeing.
If you are shooting in manual mode, you can just change aperture, shutter speed, or your ISO to either over expose or under expose. For instance, you are shooting a very bright scene like a snow covered mountain. The camera will try to darken the scene to bring it back to 18% grey based on the assumption that ALL scenes can be reduced to 18% grey. To correct this, you actually have to over expose the image (let in more light) to force the camera to depart from the 18% grey to match the actual scene. You would just have to play with it to determine the right amount of over exposure. If you were shooting in one of the program modes or scene modes in the camera, then you would use the exposure compensation control to do the same thing.
Likewise, if you are shooting a scene with a lot of dark areas, the camera would try to over expose to brighten the image and bring it back toward the 18% grey. You would either have to adjust aperture, shutter speed, or ISO to reduce the amount of light coming in, or change the exposure compensation to under expose.
At first it might seem kind of backward that you have to let in more light for a bright scene and less light for a dark scene. But it helps to remember than the camera is trying to pull the scene back to that 18% grey and you have to counter that action. Also, remember that it is not about how much ambient light you have, but rather what the colors tones are in the scene. In low light, you will generally have to let in more light to get a good exposure and with lots of light you may generally have to crank down on the amount of light coming in to get a good exposure. This is more about the reflected light coming off your subjects.
There are TONS of articles, blogs, and videos on the subject.