Since its original publication in 1962, Lorrain and Corson's text has offered physics and engineering students a formula for developing a working knowledge of the basic principles of electromagnetism. The formula is practice.
Honestly, E&M is one of the most difficult subjects for me within Physics. This book did a good job helping to untangle the knotted yarn ball of E&M to me.
A unique presentation of special relativity which is completely and inexplicably missing from the undergraduate curriculum. You can't understand how electricity and magnetism are related in a non-relativistic framework.