As with all baristas, I have my own method of making a great espresso. To start with the water must be fresh. Water can be affected by poor cleaning habits, mildew or filtering issues. It has to be the correct temperature, which is around 203F (95C)
For the best quality coffee, I recommend Arabica which is produced in Bogota, Brazil or wherever it can be grown 3000ft above sea level. You can use Robusta as a last resort but it is less flavorful and has more caffeine. Whether you buy it roasted or you roast it your self, it must have that fresh smell when you open the container a few days after.
Use a burr to grind your coffee not a blade grinder. Blade grinders chop the beans whereas the burr grinders have triangular teeth on two plates that grind the beans between them. How fine the beans are ground depends on the distance between the two plates. A sand grain is perfect but a powder is too fine and gravel too coarse. Make sure to minimize the coffees exposure because it absorbs any odor that happens to be in the air.
You will need a good machine. A good espresso machine generates heat using a boiler or a thermablock and can pump pressure of 9 bar or...