Get into the habit of summarising. Read a short passage - whatever you like, and then write down the gist of it in a few sentences. Or think of a film you've seen or a book you've read and imagine you have a minute or so to tell someone what it's about.
And read - fiction, travel reviews, journalistic pieces - as full a spread of different types of writing as you can. A quality newspaper's Sunday supplement would be a good starting place, as well as some novels, poems or short stories. As Mosaic suggests, it could be worth contacting you tutor, if you can, to see what texts he or she will be using for the course. However, when I taught this course to adults, I usually compiled a shortlist (because the exam boards usually give a range of texts to choose from) so that we could discuss and decide as a group what they wanted to study.