Oxygen is the biggest enemy of coffee, and if left exposed it will stale in 12 hours! Make sure once the bag has been opened it is sealed again tightly away from strong smelling foods.
Get the Grind right. It is imperatives that the grind of your coffee beans is correct – too fine or too coarse can have a real impact on the taste and quality of the coffee you serve. Normally it should take around 25 seconds to pour an espresso – if you are not hitting this every time, check your grind is correct.