Espresso preparation uses pressure to move hot water through a prepared bed of ground coffee. Machines achieve control in different ways, so begin by understanding your own equipment and its instructions rather than copying an unrelated setup's numbers.
Use coffee you want to drink and grind for the basket and machine involved. Measure the dose, distribute the grounds consistently and tamp level. Record the resulting beverage mass and brewing time so the shot can serve as a reference rather than a one-off attempt.
Taste before changing the recipe. If you adjust grind or output, hold the other relevant variables steady enough to understand the result. A dark roast is one possible choice, but the word espresso describes preparation rather than a requirement that all beans be roasted to the same color. A repeatable sequence will help you explore different coffees more effectively than treating a single traditional serving volume as the definition of every successful shot.
The conversation
A good question can make a better brew.