Computer Science - a Modern Introduction . You should also try some of the exercises. In particular, the first 15 exercises at the end of Chapter 2 on the design of algorithms and the first 10 exercises at the end of Chapter 4 on computer architecture are relevant preparation for the introductory lecture courses.
Many students have some difficulty with the mathematical aspects of the first-year course.
A little study of pure mathematics would be valuable. It will also help to pursue recreational mathematics in the form of games and puzzles to keep your skills tuned. General reading After the technical reading suggested above, the next most important preparation is to build up a broad background understanding of current issues in Computer Science. The New Turing Omnibus . Computer Science Press.