When building any type of paid search campaign, the structure of it is the base of how well it will perform. One of the major mistakes people make is to have one campaign with multiple keywords.
Most paid search networks allow you to create multiple campaigns, mainly for the purpose of keyword and campaign relevancy. Also you can break out your keywords into more specific ad groups. By having separate ad groups you can tailor your ad copy to the particular keywords that are placed in that group.
By structuring your campaigns this way, you have a better chance of increasing your campaign’s performance.
When campaigns are lumped together into one, it can confuse the searcher. Although your keyword is typed, by not having it in a specific ad group, any ad of yours could be served to the searcher. As the ad groups are more closely tied to the ad copy, the message sent to the searcher is more precise and clear. By using tools like Google’s AdWords Editor, breaking out campaigns can be fairly simple.