There are four main steps in making a great coffee: the grind, the pour/extraction, texturing/heating the milk, and then pouring the milk.
The grind is the first step a lot of people fall over. Many have the grind level set by the coffee company or service man, then never adjust it.
The grind needs to be set every day, since the weather (e.g. humidity) can have an effect on the grind. A good barista will check the grind each morning by making a few coffees before the store opens and adjusting the grinder accordingly. Throughout the day, the barista will continue to make minor adjustments. I will go into more detail soon.
Now the pour partly depends on the grind and the “tamp.” Most machines are automatic these days, so the size of the shot of coffee should be already set and therefore will not be a variable at this stage. Now you want to end up with a beautiful golden even-looking crema, the golden-brownish foam that covers a freshly-brewed cup of espresso, created by the high pressure of the water being forced through the coffee grounds. If your coffee does not have this golden crema on top, you need to start again, as your coffee will not be nice at all—it will be either bitter or weak. Again we will go into more detail in the next section.
The milk needs to be smooth, silky, and not too hot. Like the grind, this is a step that many people fall over. They end up with a airy bubbly mess of boiling-hot tasteless milk that ruins the coffee.
Each of these steps is just as important as the other, and all need to be perfected to make a truly great coffee: the kind of coffee that you will come back time and time again to experience.