Arguably one of the most influential, and hard-to-find books "Breakthrough Advertising" was written by Eugene Schwartz. For many years this book was completely unavailable. There was even a black market for this highly coveted book, with copies selling in the many hundreds - sometimes thousands - of dollars. I paid the former amounts to get my copy ... and it's paid me back many times over. If you can get a copy today, I recommend without reservation, you get one ASAP! And study it like your business life depends on it.
Here's a 2 page summary of some of the training contained within. Most people screw up their advertising because they don't understand the 5 stages of advertising development. Print this document and study it closely ... your advertising sales will increase directly from application, I assure you.