Every session

After each coffee

From the manual's cleaning section.

1. Take the filter out of the filter holder and wash both in warm water, every day.
2. Brush any coffee grounds off the shower screen and rinse it with hot water.
3. Wash the drip tray and grid. The manual says not to use abrasive tools.
4. Keep the clean filter holder on the machine, without tightening it too much.

A few drips from the group after you take the filter holder off are normal. The manual puts them down to the water pressure in the system.

Gaggia Classic E24: every job