Of course, you don't want to be paying for Web traffic that has nothing to do with your business. You want to find targeted keywords that will lead to a higher PPC click-through rate, effective cost per click, and increased profits. That means the keywords you bid on should be closely related to the offerings you sell.
PPC is iterative. You want to constantly refine and expand your campaigns, and create an environment in which your keyword list is constantly growing and adapting.
Your keyword research should include not only the most popular and frequently searched terms in your niche, but also to the long tail of search. Long-tail keywords are more specific and less common, but they add up to account for the majority of search-driven traffic. In addition, they are less competitive, and therefore less expensive.
Crafting relevant PPC keyword lists, tight keyword groups, and proper ad text.