To prepare for Calculus III after completing Calculus II, it's essential to familiarize oneself with mathematical proofs, as this foundational skill will ease the transition into more abstract algebra concepts. The Algebra sequence is often challenging, and starting with courses like Modern Geometry, Linear Algebra, or Elementary Number Theory can provide a smoother bridge to proof-based mathematics. Engaging with proof problems in Elementary Linear Algebra is recommended, along with independent study in number theory to enhance understanding and ease the learning of algebra. "Elementary Number Theory" by Jones and Jones is suggested for its clarity and comprehensive solutions, making it suitable for self-study. Additionally, Pinter's book is recommended for its accessibility and introduction to algebra concepts. Reviewing resources like Marsden's free Calculus III book can also help in understanding what to expect in the upcoming course.