The heart of any successful Pay Per Click campaign is using a focused keyword lists. It is absolutely critical that you break down your main keyword lists into smaller lists that are focused around subtopics.
If your ads are not targeted to your keywords (i.e. a general purpose ad on insurance showing up for someone who is searching for car insurance) people might not click on your ads. Worse, if your site does not offer a particular type of product (you’re targeting custom home theater systems when you don’t offer any customisation), all those clicks will be wasted.