A couple of weeks ago I told you that your first negative keyword lists  should consist of your brand keywords. Doing so keeps your competitive (higher CPC), non-branded campaigns from poaching brand-related ad impressions.
Typically we see negative keywords  being used to stop ad impressions from completely irrelevant search queries (or search queries that bring no business value), but there is a case for using relevant keywords as negative keywords.
Using brand-related keywords in negative keyword lists is not the only example of using relevant keywords as negatives. Depending on your business, you may find, after analyzing your search query reports, that your campaigns are poaching ad impressions from each other.
Because of this, I recommend that you create a negative keyword list for each of your major campaigns in your AdWords account.
For example, let’s say that you sell pet clothes for both dogs and cats. You may have both a DOG CLOTHES and a CAT CLOTHES campaign running in your account. Most likely, you have broad match keywords that may compete for the same ad impressions across campaigns.
The only way to prevent Google from choosing to serve an ad to the wrong search query is by explicitly telling them not to do so with a negative keyword. Otherwise, they enjoy the freedom you’ve given them by choosing to use broad match keywords.
To get your lists started, I would take the top exact match keywords in your campaigns and create a negative keyword list for each of your campaigns. Here’s what those lists might look like for the DOG CLOTHES and CAT CLOTHES campaigns:
Now depending on how closely related your campaigns are, you may have to experiment with using different negative match types. In the example above, you should be safe using negative broad match keywords.
Next, associate your negative lists to all the other campaigns in the account (that might be an ad poacher) for each campaign. In order to do this you have to navigate to the bottom of the keywords tab for each campaign (don’t get me started ) and open up the "Negative keywords" link.
The end and desired result is that Google can’t serve a "cat clothes" ad to a "dog clothes" search query because the only ads eligible to serve are in your CAT CLOTHES campaign.
Now once you have these lists in place within your AdWords account, regularly take the time to drill into your search term report located in the "Keywords" tab.
Add any ad poaching search queries that you find directly to your negative keyword lists.
Now sit back and enjoy getting Google to serve the right ads for the right search queries. Of course, you can push this same concept to the ad group level for even tighter control, but that’s a more complicated topic for a future post.
By Chad Summerhill, author of the blog PPC Prospector, provider of free PPC tools and tutorials, and in-house AdWords Specialist  at Moving Solutions, Inc. (UPack.com  and MoveBuilder.com ).