To make the best shot of espresso I know how:
1. Start with the best, freshest espresso beans you can find. Alakef Roasteries in Duluth is the supplier of the shop I used to work at.
2. Grind the beans right before you make your shots.
3. Fill the basket with ground so it's even with the top, then tamp it down under about 25 pounds of pressure. (Some grinders have tampers built on, and you lift the basket into the tamper. For these, it's properly tamped when you barely lift the grinder.) If you tamp it too much, the water will not go through the grounds, and if it's not tamped enough, the water will run straight through.
A good shot will take about 20 seconds from start to finish (18-22 is usually acceptable), and the stream should be a smooth, constant drizzle. This has been likened to a rat tail, if this helps you picture the stream. Just picture a smooth stream coming from your kitchen faucet. It should look like that, only smaller. If a shot is too short or too long, there are two things to do:
1. If you are tamping by hand, change how hard you tamp, tighter if the shot was short, ligher if the shot was long. If you are using the tamper on your grinder, or you know you are tamping the proper amount, DO NOT TAMP HARDER OR LIGHTER.
2. Adjust the grind of the espresso beans. There is a knob on most commercial grinders which you can turn to adjust the distance between the burrs in the grinder. The grind and consistency of the espresso grounds varies with temperature, humidity, and quality of the beans. Again, if the shot was fast, make the grind smaller. If the shot was slow, make the grind larger. Once this is perfected, your shots should turn out perfect every time. Enjoy!