The keys to good espresso on a semi-automatic or fully automatic machines are:
1. Quality of Bean - Get the best you can find. I would find a local coffee shop or roaster whose coffee you like. Don't go with the Starbucks, etc. or grocery level if you can avoid it. Those tend to get stale quickly.
2. Roast - Nothing beats home roasting, but that adds a new level. Be sure to pick up "espresso roast" (espresso is in the roast, not the bean).
3. Grind - Definitely get a good burr grinder. Your grinder is your best friend. The grind should be coarse like sand. If you don't have the means to get a good grinder, get it ground at the coffee shop. Keep in mind, ground coffee will only stay fresh for a few days.
4. Tamp - You should put 30 pounds of pressure when "tamping" (pressing) the espresso. Test on a scale.
5. Water - Use distilled water.
That's it! You'll be on the road to making espresso's that can beat anything you can buy at a shop.