How do I learn the Preterito Indefinido?

Learn using sample sets. It helps enormously. Create a set to jdm irregular verb that you can remember well. Also learn the signal words that trigger indefinido by heart. Very important are that you notice the endings of the three conjugation classes ar, ir and him.

First learn the irregular forms you use most often like e.g. by ser, ir, estar. Try not to learn at once, but limit it. For example, can also form topics fields.

Doing Indefinido needs time and patience, but it will work:)

I hope I could help you a bit 😊