Depends which question you're doing- for child acquisition questions context such as relevant theories and studies like Bruner and Vygotsky, Piaget, Skinner, Chomsky- but also less obvious ones such as the Fis phenomenon, Genie case study
For language change questions there are so many things to include, historical info about the century the text is from, David Crystal, attitudes to language change (Damp spoon, crumbling castle, infectious disease), change models (Kachru, Stages of colonial English etc)
Cant really be very specific because you were quite vague and idk what you specifically need to improve on so theyre just a wide range of topics to be including and referring back to regularly