This is probably the most concise espresso brewing guide. It teaches you in two minutes how to make coffee with a semi-automatic espresso machine. Pulling shots like a professional barista is not as hard as it seems. You just need to understand all the preparation aspects and follow the recipe.
Use good quality water, tamp with 30 pounds of force, grind coffee just before brewing, and use the correct amount of coffee beans, (you need a scale). If you follow the infographic’s instructions you are guaranteed to get decent results at least. Sure, you can always improve, and there is more to learn about espresso, but even if you are perfectionist this is great starting point.

Infographic by how to make espresso