How can I tell when to use 'ser' or 'estar'?

These two verbs are often confusing for students of Spanish as the split of 'to be' into two verbs is not seen in English. Therefore, it's important to have a quick method to accurately decide which verb is the correct choice in a given phrase. The acronym PEPE covers most of your bases and lets you know when 'estar' is the correct choice.P = PosiciónE = EmociónP = Presente continuo/progresivoE = Estado

'Posición' refers to physical location, be it permanent or temporary. For example, 'mi casa está en Londres' and 'Juan estaba en casa hace una hora' are both correct even though 'ser' is often erroneously selected in the first case, since students often assume that permanence selects 'ser'. 'Emoción' refers to someone's current, temporary state of mind, as in '¿estás muy aburrido, no?' or 'Raquel está cansada'. Note that '¿eres muy aburrido?' means that you are an easily bored person, whereas the version with 'estar' means that at this current moment you are bored. 'Presente continuo/progresivo' is the easiest to remember, since phrases like 'estoy jugando al fútbol' are heard very often, and 'eres jugando al fútbol' is grammatically incorrect, with no room for choice. Lastly, 'estado' is similar to 'emoción' in that it refers to the temporary physical state of a person or object. So 'mi traje está sucio' means that the quality of being dirty is not permanent for the suit, i.e the suit is not characterised by always being dirty. All in all, this acronym will help you when you're in a pinch and need a quick reminder of the reasons for using 'estar' over 'ser', but it's always best to try and internalise these rules and eventually make the thought process instant through exposing yourself to Spanish via TV, books and movies.