to do complex analysis, you need to understand continuity, integration theory, power series, and some plane topology. Some courses will try to teach all this in the course, but it helps to review your Riemann integration, and not just as antidifferentiation, but as limits of Riemann sums, especially applied to path integrals. It also helps to understand stereographic projection, e.g. lines and circles in the plane and their relation with circles on the sphere. One also usually makes more use of differentials, things like dz, dx, dy than in real calculus. And review your partial derivatives, and green's theorem from advanced calculus. Of course review algebra of complex numbers.