Look at any good book about, or take a class in discrete math, probability and linear algebra. Those are the subjects that stand out for me. Discrete math is th

Look at any good book about, or take a class in discrete math, probability and linear algebra. Those are the subjects that stand out for me. Discrete math is the most fundamental for computer science. That Concrete Mathematics book looks promising - plus it's got some information about algorithm analysis and other computer science specific topics. You should take a class in discrete math, or if you're disciplined enough, start with that book.