Pick any magazine.
Then have someone read just the advertisements out loud.
Then, and this is the important part, see if you can tell what the ad is for.
Who's the audience?
What's the message?
What do they want you to do?
It'll only take one magazine (of choice) to see just how important answering those three questions really is to your advertising. You could probably do the same with TV, but I don't watch it much so couldn't say.
And if I saw this little exercise here on WF then sorry for sharing your secret, but damn that was cool!