If your ad's not pulling like you want, the culprit most often is your headline (assuming your market wants what you're offering and the media you are using is proven reliable).
I've been re-reading a classic advertising book and it's reminded me of the importance of headlines in ads.
Eugene Schwartz, author of #1 classic "Breakthrough Advertising," says your headline must capture the preeminent desire your audience has... Your headline, Mr. Schwartz's words, must...
Acknowledge that desire - reinforce it - and/or offer the means to satisfy it - in a single statement in the headline of your ad