How do I know when to use "être" or "avoir" to conjugate in the perfect tense?

In English, the perfect tense always requires the auxiliary verb "to have", but in French, you will need to use either avoir (= "to have") or "être" (= to be). Most verbs will require "avoir". The minority of verbs requiring "être" are summed up in the mnemotechnic device "MRS. VAN DER TRAMP", which stands for:-         Monter-         Rester-         Sortir -         Venir-         Aller-         Naitre -         Descendre-         Entrer-         Rentrer -         Tomber-         Retourner-         Arriver-         Mourir-         Partir All derivatives of these verbs (e.g. revenir, devenir) will also need "être". Finally, all reflexive verbs will need "être".