The spot metering is programmed to deliver ideal exposure for a 18% grey subject. So if your subject is white, you need to introduce an overexposure correction that leads to the white aspect, if your subject is black an underexposure correction is necessary to get the black aspect.
To make it simple, using efficiently spot metering consists IMHO in selecting with accuracy and with time experience the tiny area that will give you directly the right exposure with no lost of time, with no exposure correction in addition, no matter your subject is.
Just have in mind using efficiently spot metering does not guarantee you will be reactive enough as you have to focus & meter the tiny area you choose, introduce exposure correction if necessary, recompose and finally shoot your picture. Choosing what PAMTv mode to use, accordingly to light conditions, is important and helpful too.