I chose my A Levels by looking ahead to what I might like to do as my degree and made sure I chose subjects to meet the entry requirements (luckily for me, Law does not require any specific subjects).
I then looked at what I enjoy doing at GCSE and what I think I would be good at at A Level and I basically made my decision that way.
I took Business last year (AQA) and we learnt about things such as quality control, operations management, managing HR including theories and methods of motivation, business objectives, marketing strategies, etc.
I also took English Lit (again AQA) and we studied tragedy last year, reading Tess of the d'Urbervilles, Othello and Death of a Salesman, as well as doing some poetry work. This year the theme is political and social protest writing, so we're reading The Kite Runner, The Handmaid's Tale and some Blake poetry, as well as doing some coursework on the literary canon and Rossetti's poetry. However, the specification includes other books as options so you may not study the same books even if you have the same exam board.