Use Mrs Vandertramp as a easy way to remember the verbs that take être as it's stem in the past tenses! Many people who are learning French find it difficult to remember which verbs take être over avoir, using this simple phrase, you can learn the verbs and their past participles with ease.
M - Monter - past participle - monté
R - Retourner - past participle - retourné
S - Sortir - past participle - sorti
V - Venir - past participle - venu
A - Arriver - past participle - arrivé
N - Naître - past participle - né
D - Descendre - past participle - descendu
E - Entrer - past participle - entré
R - Rentrer - past participle - rentré
T - Tomber - past participle - tombé
R - Rester - past participle - resté
A - Aller - past participle - allé
M - Mourir - past participle - mort
P - Partir - past participle - parti
These verbs take the être form when put into the past tense. These verbs also take on agreements depending on the nature of the pronoun such as feminine and plural. Also remember that reflexive verbs (verbs such as 'se laver') will also take the être form.
For example 'Partir'
Je suis parti(e)
Tu es parti(e)
Il/elle/on est parti(e)
Vous êtes parti(e)(s)
Nous sommes parti(e)s
Ils/elles sont parti(e)s
An example of a reflexive verb 'se laver'
Je me suis lavé(e)
Tu t'es lavé(e)
Il/elle/on s'est lavé(e)
Vous vous êtes lavé(e)(s)
Nous nous sommes lavé(e)s
Ils se sont lavé(e)s
By using MRS VANDERTRAMP, you should be able to remember all these verbs easily so you know when a verb take être over avoir.