Brush up on your PDE's, Green's functions, the method of images, and vector integral theorems. You might also brush up on your complex variables. Jackson never explicitly invokes them but several of your homework solutions will be shortened by pages if you know how and when to use those methods.
Thank you for the input.
for Vector Calc and image problems I'm using griffiths, for PDE i'm using Boas, for Green's Functions I'm using Byron and Fuller (Mathematics of Classical and Quantum Physics).
Are there any other resources anyone can suggest?
Boas also has a (rather short) section on Green's Functions. For getting vector calc down solid I reccomend Div, Grad, Curl and All That by H. M. Schey, you can get it pretty cheaply (although it isn't a Dover book) and he does a very thorough treatment.