How do I know which verbs take 'etre' and which verbs take 'avoir' in the past tense?

The best to learn which verbs take 'etre' is through MS VANDERTRAMP. (Then I would explain what each letter stands for). After this I would remind the student of compound verbs. For example, entrer is a verb that takes etre, but rentrer is a compound verb of entrer, and would therefore also take 'etre' in the past tense. All other verbs take avoir.