I think it is mostly common sense. A pinch is what is between two fingers. To taste is what you like it to taste like.
A glug is one big dollop of liquid coming out of the carton (a mouthful). A handful is whatever the size of a normal adult hand. You can tell if an onion or potato is small, go from there. A heaping teaspoon is ingredient piled as high as it can go without spilling over. A rounded teaspoon is ingredient rounded off to fit the spoon. That is how I would measure all of these.