I get a lot of questions from customers about what to test, and especally what to test first. There is a very simple rule of thumb here. Almost always, your headline will have the greatest impact on overall conversion rates. A great headline can literally make or break your campaign, so start here.

The esteemed John Caples, author of “Tested Advertising Methods,” estimates the headline makes 50%-75% of an ad. Must be why he spent and entire 5 chapters on headline writing and testing alone. If you don’t have this book on your shelf now, and you are serious about improving your online sales copy, I suggest you get it immediately. It’s probably the smartest fifteen bucks you could spend.