According to Mitch Meyerson and Mary Eule Scarborough, authors of the book "Mastering Online Marketing", PPC marketing campaigns such as Adwords allow website owner to set advertisements on results pages after a simple keyword research. Which means that you agree to pay for traffic according to a person's keywords.
In order to make this effective, it is important to display your ads only on search engine results which can normally generate the type of traffic you are looking for. This can be an easy thing to to if there is a particular phrase or keyword that people look up to find services or products you are offering, but it's a bit trickier when there are synonyms for your keywords, or when adding a single term before or after the keyphrase can alter the meaning.
For this reason, many Adwords master like Perry Marshall encourage pay per click managers to undertake something called 'negative keyword research'. This requires making a keywords list that you don't want to include as part of your marketing campaign, because you have reason to think that the type of traffic that these keyword searches would generate will not convert for your specific product. This negative keyword strategy can save you money and ensure that your advertisements will only be shown to visitors who may be high converters.
Another way to generate more traffic with PPC campaigns is to monitor your click through rates on a regular basis and find out which specific phrases or words within your advertisements are converting. If you're using Adwords, you can link your account to your Google Analytics account for simple monitoring of every click. With these statistics, you will know what individuals are searching for one they see your advertisement, and whether if they're clicking through to your service or product after seeing your advertisement.
Finally, it is important for all the PPC marketers to tweak and modify their own ads based on performance. It is generally a wise decision to run several ads using the the same keywords but different headlines and descriptions at the same time, and find out which ones are performing better than the rest. This can help you narrow down the high-converting ads as well as help you to concentrate your investing in just the words and ads which are getting results.