Which verb should be used, "ser" or "estar"?

In Spanish there are two verbs that translate to English as "to be", and it can be difficult to know the contexts in which to use each one. But I've found that the acronym DOCTOR SELF is very helpful in remembering where each verb should be used in Spanish. DOCTOR tells us where "ser" can be used: in Descriptions (eg "es muy bonito"); when talking about Occupations (eg "es médico"); to describe someone's Character (eg "es amable"); for the Time/date (eg "es lunes"); to talk about someone's Origin (eg "es de Alemania"); and to describe Relationships between people (eg "es mi marido"). We use SELF for "estar" contexts: when describing a State of being (eg "estoy cansada"); an Emotion (eg "estoy triste"); to give a Location (eg "está cerca de mi casa"); and when talking about a feeling (eg "estoy relajada").