When using the passé composé (present perfect tense) how do I know whether to use avoir or être as the past participle?

It can certainly be confusing when first learning the perfect tense, whether to use avoir or être as the past participle. For example why do we say 'Je suis venu(e)' - taking the être form, rather than j'ai venu(e). Equally it is correct to say 'J'ai mangé(e)' rather than Je suis mangé(e). There are 16 verbs in French which take the être form, a good way of remembering this is DR MRSVANDERTRAMP - the verbs stand for Devenir Revenir Monter Rester Sortir Venir Aller Naître Descendre Entrer Retourner Tomber Rentrer Arriver Mourir Partir.
Each verb in the acronym above takes the être form, all other verbs take the avoir form in the perfect tense. In both cases, it is necessary to use the conjugation + the past participle of the verb. See below the conjugations of avoir and être in the perfect tense:AVOIR + past participleJ'ai, tu as, Il/ elle a, nous avons, vous avez, ils ont
ÊTRE + past participleJe suis, tu es, il/ elle est, nous sommes, vous êtes, ils sont
Another tip to remember is that avoir is often used to describe action verbs and être is used for verbs describing a state. Let us run through some examples now.