When choosing placements, focus on the following:
* Use relevant keywords for automatic placements and to further refine your managed placements.
* Using keywords to refine the targeting for your ads on placements is a good option when you're targeting sites that have a wide variety of content (such as news sites and social networks). That way, your ads will be more likely to appear in relevant locations on those sites. Adding keywords will also limit the potential number of clicks and impressions, so you should monitor your ad's performance to make sure you're seeing the results you want.
* If you want contextual targeting to be the only deciding factor in where your ads appear, you should create a keyword-only ad group.
* If you want your ads to show anywhere on a given placement, with no regard to contextual matching, then create an ad group with placements only, and set your campaign settings to "Relevant pages only on the placements I manage." That way your placement choices (and the AdWords auction) will be the only factor involved in where your ad can appear.
* Select placements that reflect your target audience and which reach your users on sites they are most likely to visit. For example, if you want to sell video game equipment, you may want to target placements that appear under the Video Game category.
* Try creating rich media and display ads and selecting sites that allow these ad formats in their placements. For example, if you've created an image ad for your campaign, you can target those ads to placements that accept image ads.
* Take advantage of targeting different types of content within the Display Network. Beyond text content, many websites contain engaging user content such as videos and games. Try targeting your ads to your potential customer by reaching them through the types of content they might enjoy. For example, if you sell a video subscription service, you might create a video ad for your product and target the ad to sites like You Tube.
* If you think you'll be using managed placements mostly to manage sites on which you want to be highly competitive, consider raising the managed placement default bid. This will give you a stronger chance at winning the ranking auction.
Source: Google adwords