When do I use the perfect and imperfect tenses in German?

A common mistake amongst English natives when speaking German is the over-use of the imperfect tense (also called the preterite or the simple past tense). For example: "Ich aß einen Apfel", "Ich las ein Buch", "Ich trank eine Tasse Tee".This tense is usually reserved for written contexts such as newspaper articles and novels. You can think of it as the 'story-telling tense' - one that's used to talk about one-time events that happened in the past.The perfect tense is more commonly used in German than it is in English to describe events that took place in the past. This tense has two parts to it, the auxiliary verb (or 'helper verb') and the past participle. For example: "Ich habe einen Apfel gegessen", "Ich habe ein Buch gelesen", "Ich habe eine Tasse Tee getrunken". Most often, these sentences can simply be translated as: "I ate an apple", "I read a book", "I drank a cup of tea" (as opposed to "I have eaten an apple", "I have read a book", "I have drunk a cup of tea"). A common translation mistake would be to assume that these sentences always mean "to have done something", rather than simply "did something". Particularly in spoken language, the use of the imperfect tense is quite rare. The only verbs that are actually more commonly used in the imperfect, rather than the perfect, are haben and sein, and the modal verbs (können, müssen, wollen, sollen, mögen, dürfen). For example: "Ich hatte", rather than "Ich habe ... gehabt"; "Ich war", rather than "Ich bin ... gewesen"; "Ich konnte", rather than "Ich habe ... gekonnt".