Dave,
It's entirely dependant on the subject of your shot - what's prompted your question?
With a standard photo of a couple at a wedding - her white dress, him black suit, the camera's reading will vary considerably depending on whether you're pointing at his black suit, her white dress, their faces etc.
I like to set the exposure manually by using the camera's light meter on an object which is as near to 28% grey as possible and not shiny - green grass is a classic example of a good thing to meter from at a wedding.
Modern 35mm neg film is extremely flexible, allowing for significant miscalculation.
Also with metering, the subject is often lit differently to the background, you'll want to make really sure that you meter from the object you wish to be lit correctly, not the whole scene as an average.
Try switching your camera to spot, not matrix or multi or 80:20 metering and looking at the readings you get for the subject specifically as a start.
Rob