By default, when you create an ad it's automatically filled-in with the title and description of your website. Now, that's all fine if you gave some thought to them when you first created your website. If, however, your title is something like “My great website” (whether or not it is preceded by the words “welcome to”) and your description similar to “This is where you'll find out all about me!!!!”, odds are no one is going to click your ad. At least not me.
On the other hand, a title like “Discount plumbing supplies”, coupled with a description along the lines of “Best brands, best prices, free delivery this week only” is much more likely to get you clicks. So remember to think about the text you use, and choose words that sell.
You'll also want to ensure you've correctly chosen your website category (Site > Website info from your site manager). This will help us target your ads correctly - after all, you don't want your plumbing store ads appearing on “Society > Paranormal” websites. Unless you sell DIY ghost-busting kits.
A few moments now can save you a lot of time (and money) later. More importantly, it will ensure you get the kind of traffic you want, quickly.
* Thanks DS for the inspiration for the heading.
** If anyone has a better-sounding e-age equivalent of “pen to paper”, please leave me your suggestion.