I plan to do a much larger post specifically on some of the ad networks later on but after a Twitter exchange today I wanted to write a short post about setting up an ad campaign. I've had some moderate success with ad campaigns using Project Wonderful so I feel like I have learned something about what works and what doesn't.
DO target sites or keywords related to your business such as: handmade, etsy, crafts, jewelry (if that's what you sell), or bath and body (again if that is your product type).
DON'T target an unrelated keyword just because it's popular. Project Wonderful has a lot of web comics offering advertising space so "comics" is a very popular keyword. However if your products are unlikely to appeal to comic readers you're wasting your money using that keyword. I sell cephalopod related jewelry so I do advertise on some comics with octopus, squid, or Cthulhu as characters because people who like those types of comics are likely to also like my jewelry.
DO monitor where your clicks are coming from, a site that sends you a lot of visitors (especially if those visitors also shop) is worth extra to keep your ad on the site. This only works with a service that allows you to select specific sites to advertise on though.
DON'T keep your ads on a site that isn't sending clicks. It doesn't matter how many pageviews it gets, if no one is clicking on your ad then it's not worthwhile.