To make a rich and velvety crema on your espresso shot, follow these steps:

1. Use fresh and high-quality coffee beans: The quality and freshness of the coffee beans are essential for producing a good crema. Choose high-quality beans that have been recently roasted and grind them just before brewing.

2. Grind the beans finely: For a good crema, the coffee grounds need to be fine and evenly ground. Use a burr grinder to ensure a consistent grind size.

3. Tamp the coffee grounds correctly: Tamping is an essential part of espresso brewing. Tamp the coffee grounds firmly and evenly with a tamper to create a compact and level coffee puck. This helps to ensure that the water is distributed evenly through the grounds and results in a good crema.

4. Use the right water temperature: The water temperature should be between 195°F and 205°F (90°C to 96°C). Too low temperature will under extract the coffee, and too high will over-extract it.

5. Brew the espresso shot for the correct amount of time: The ideal extraction time for a good crema is between 25 to 30 seconds. If the extraction time is too short, you may not get a crema at all, and if it is too long, the crema may become bitter.

By following these steps, you can make a delicious and velvety crema on your espresso shot. Remember to practice and experiment to find the best technique that works for you and your machine.