Sandy and for others
I use manual metering for 99%, I don't have to think that way.
If you use auto there are many elements that come into play that may change exposure.
I prefer to watch facial tone and adjust while shooting to keep that consistent.
That way the background / foreground or anything else becomes second priority
When I do use auto, I select shutter priority and let camera pick aperture.
The metering is set to center weight and I fill most of that area with subject I want exposed.
If you use spot - it will look at exposure in smaller area, which can work. I just prefer more area for exposure.
When you select matrix or average all - it takes into account fore and background light difference and want to balance.
A dark background and brightly lit Joe would over expose his skin tone and washout texture.
Hope that helps.
Fotopete