How to improve mathematical skills for Electromagnetic and antenna field?

Hello every one. I have one trouble relating to mathematics.

Recently, I recognized that It's very difficult to make new ideas or solve complex problems without good basic of mathematics.
I found some very interesting journals in field of antennas, and authors used a lot of mathematical knowledge and programming. I cannot understand them.

Can I ask you how to develop mathematical skills and programming skills in the field of EM and antenna? What are the necessary tools (Ex: FDTD, FEM...) ?
Is there any good book or good method that you have known?