Iterate, iterate, iterate: constantly tweak and monitor your PPC campaigns.

Like search engine optimization, PPC campaigns are not static. Your web tracking tools will help you understand which keywords are working, what new keywords are emerging, what search engines are yielding more or less visitors, and how many visitors turn into customers. Armed with this information, you should be pausing or changing old ads, working with different PPC search engines, expanding campaigns, or creating new campaigns. If you have a promotion, you should create an ad for it. If you need to allocate more resources to other marketing activities for a while, consider tapering your PPC efforts. Most importantly, keep up to date with your campaigns and do not be afraid to experiment!