As exact exposure remains a struggle for many hobbyists when it doesn't need to, it occurs to me that a few quick rules of thumb may help. While matrix metering is a handy tool, there are often better ways to meter. There's no substitute for understanding metering and exposure, but these three tips can get you an accurate exposure quickly and consistently.
Sunny 16: An oldie but goody, the sunny 16 rule is always accurate when used correctly. On a sunny day, with no interference from shade or clouds, the correct exposure for any scene is a shutter speed of 1 over the ISO at f/16. If your ISO is 100, then the correct shutter speed is 1/100 and aperture is f/16. Using the law of reciprocity, you can vary this exposure to get the same result with different settings -- for example, ISO 100, 1/200 at f/11. With this rule, you always have a perfect exposure starting point on a sunny day without having to do any metering. The best part of knowing the correct exposure for a light source is it's constant regardless of where you point the camera!
Hand-held meter: Nothing beats the accuracy of a hand-held incident meter because it gives you the correct midtone exposure for any source of light with the push of a button. It measures the light falling onto the integrating sphere of the meter and is not distracted by color or tonality of subjects. Hence, when getting a reading for a given light source, a black subject will expose black and a white subject will expose white. It takes a couple of seconds to meter and put the settings into the camera -- literally maybe five -- but the benefit is there's zero guessing and you can immediately shoot with confidence without having to chimp. To use it correctly, place the meter's sphere in the same light as the subject -- in front of the subject pointing back at the camera if possible.
Spot meter: Using the camera's spot meter to measure a subject of known reflectivity can get you an accurate starting point sometimes more quickly than using a hand-held meter, and usually more quickly than matrix metering an entire scene and guessing as to how the camera will render it. The key is knowing how to compensate if necessary. If you meter a subject known to be 18 percent gray, such as caucasian skin, the reading you see in the camera will be the exact correct exposure. This is why photographers sometimes meter gray cards. There are other ways to use this: Meter a highlight -- bright white object -- and increase exposure 2.5 stops to make sure you record as much detail as possible without losing highlight detail. This doesn't guarantee shadow detail if the scene is outside the camera's dynamic range, and it's more of a landscape than portrait technique. Make sure the object being metered fills the focus point and a significant area around it. The longer the lens, the more accurate the spot will be.
I know the camera's reflective meter is meant to give you quick results, but the problem is everything reflects differently and the camera averages everything to 18 percent gray regardless of what tonality it actually is. This leads to inconsistency, guessing, frustration and lack of confidence, and without a known subject or hand-held meter, you don't know whether the exposure is 100 percent correct or not, even if it is. With a few more exposure skills in your kit, you'll be better equipped to nail those shots perfectly every time.