The concept I chose to look for was Affordances–indicators of how the user is supposed to interact with the product. Starting with the bad example, which I’m sure almost all of us have struggled with at some time: 

The milk dispensers in the DHall. If you’re familiar with them, it’s fine, but when first encountering them, you have no idea what to do. Obviously the glass goes under the nozzle, but what is the handle there for? Is it a guard, or do you push it down or lift it up? Or do you push in on the grip thing behind? It’s just a plain metal handle. No indication of what to do with it.

In contrast, just next to it is something that has a very clear affordance:

Sorry I don’t know how to rotate it, it’s upright on my computer…anyway, the soda machine! It’s hard to put your glass under the nozzle without nudging the handle thing a little, and it clearly says “push” on it, so there’s no ambiguity. This is obviously a better design than the milk dispensers, but let’s assume that the mechanism has to stay pretty much the same for the milk dispensers in a redesign. You could do something as simple as adding a label to describe the correct action. I.e.

Or, if you wanted to really redesign, you could do something like (forgive my terrible drawing skills)

A lever like this! Both designs give clear affordances, and like the soda machine, the lever uses a familiar mechanism most people will know how to operate.