While tasting the coffee, you should try to discern whether the flavor, body, acidity and aroma of the coffee is pleasant, or unpleasant.
Here are the criteria that most tasters use to judge coffee:
Acidity is a desirable characteristic in coffee. It is the sensation of dryness that the coffee produces under the edges of your tongue and on the back of your palate. The role acidity plays in coffee is not unlike its role as related to the flavor of wine. It provides a sharp, bright, vibrant quality. With out sufficient acidity, the coffee will tend to taste flat. Acidity should not be confused with sour, which is an unpleasant, negative flavor characteristic.
Aroma is a sensation which is difficult to separate from flavor. Without our sense of smell, our only taste sensations would be: sweet, sour, salty, and bitter. The aroma contributes to the flavors we discern on our palates. Subtle nuances, such as "floral" or "winy" characteristics, are derived from the aroma of the brewed coffee.
Body is the feeling that the coffee has in your mouth. It is the viscosity, heaviness, thickness, or richness that is perceived on the tongue. A good example of body would be that of the feeling of whole milk in your mouth, as compared to water. Your perception of the body of a coffee is related to the oils and solids extracted during brewing.
Typically, Indonesian coffees will possess greater body than South and Central American coffees. If you are unsure of the level of body when comparing several coffees, try adding an equal amount of milk to each. Coffees with a heavier body will maintain more of their flavor when diluted.