Sometimes the most powerful things you can do to improve your PPC results is go back to the basics. One of the most important I've found is making sure that each Ad Group has a healthy list of negative keywords. Eliminating those useless impressions can make a big difference on your Click Through Rate, and even save you a few bucks from click-happy searchers who really didn't want your product, but clicked on you just because your ad was there.

Google makes it easiest to add negative keywords to your account. Their campaign-level negative keyword tool takes just a few minutes to add all the terms to all the Ad Groups with basically one click of a mouse. I've subsequently added specific negative keywords to certain Ad Groups to supplement my master list, but even if I don't get a chance to do that right away, I know I'm still protected from the bulk of unwanted impressions.

MSN is much easier to work with now than they were during beta-testing. Though negative keywords can only be added at the Order level, you can still cut and paste the entire list in one shot. My experience showed that with MSN this greatly reduced my number of impressions, but I'm still glad I did it because my ROI improved noticeably.

Yahoo is the only one that limits the number of negative keywords you can enter. The magic number is 90 - with 45 at the campaign level and 45 at the keyword level. Fortunately, by using the keyword selector tool, you can discover what terms are considered identical by Yahoo. For example, to Yahoo, "bill" and "bills" are the same word, but "billing" is different.

So if you don't have any negative keywords, consider building a list and entering them as soon as possible to improve your CTR. If you do have a list, when was the last time you checked it? I'm doing mine today.