The first principle for selecting materials to select and grade materials for language teaching is vocabulary. For example, in teaching inflected languages one normally starts with materials in the easiest of the noun declensions and verb conjugations in the first term of study and then gradually adds in the rest over the course of the year, usually introducing no more than one new declension or conjugation a week. Verb tenses and moods should also be added gradually, with the subjunctive and other less frequent used aspects taught in the second or third term. Next, one chooses works using increasingly complex clausal structures. Reading passages should mirror the vocabulary and syntax to be taught each week; many graded readers are available for most languages, but for advanced students, one can select literary passages that are appropriate to the language skills of the particular grade of learner you are teaching.