I don't think anybody can say with precision when and how to shift . Like someone said, it is more of an art than a mechanical thing.
I have never ask myself '' OK now, is it time to shift or should I wait, or let's look at the tach, do I let it go for an other 1397RPM wait, no let's shift''. It has to be a natural thing, if you're in tune with the car, the road/traffic conditions, your next move, your right/left feet.
Just imagine a truck driver having to deal with 14/17 gears. Can you imagine his brain going through this motion.
Shifting in normal conditions has to be as natural as walking down the street.