Okay, I know that you can use a spot meter to place values, but a center weighted meter pretty much evaluates the whole scene and averages for the value at the center. So with that information, how do I learn how much compensation I must apply for certain situations?
Example: backlit portrait, I know I'll need to open up (and with a spot meter, I would meter the face and open up 1 stop), but how much/how do I determine how much?
In a nutshell, note-taking and experience are key to repeatable results. Anyone can get lucky occasionally but repeatable results under varying light conditions are the objective. Not all center-weighted meters are the same; some are 80/20 (Nikon F3) while many are 60/40 so knowing your meter is important. If the scene permits, try approaching a particular portion of the scene to essentailly spot-meter it and only it before making exposure adjustments and returning to original vantage point for framing.
In your example, I'd 'spot-meter' the face by moving closer as mentioned above, or using a longer lens (and transferring the settings to your shooting lens) if you don't want to stick your camera right in their face. Make note of how much your 'spot' reading deviates from the reading of the whole scene, and you'll get an idea of how to adjust without having to move in next time.
Okay, I know that you can use a spot meter to place values, but a center weighted meter pretty much evaluates the whole scene and averages for the value at the center. So with that information, how do I learn how much compensation I must apply for certain situations?
Example: backlit portrait, I know I'll need to open up (and with a spot meter, I would meter the face and open up 1 stop), but how much/how do I determine how much?
Experience is the short answer. Shoot and print. Shoot and print. Shoot and print.
For the back lit portrait I'd just move up close to the subject to meter so that the only thing in the frame is the subject then open up like with a spot meter.
Another option is using the sky as a reference point for the direct camera setting.