As you read them, pick out the various persuasion components.
Joe Karbo's famous ad is a good example ...
Popular Science - Google Books
Notice how the headline and subhead grab the reader's attention with incongruency. The ad also has excellent social proof, credibility, and uses a 31-day hold.
And interestingly, a significant portion of the ad addresses objections.
Okay, here's the caveat. The space ads of old were limited to the size of the magazine page and didn't contain all the components necessary to sell successfully on the web today.