The document discusses principles for choosing keywords for pay-per-click (PPC) ad campaigns using an analytical approach. It presents data on keyword search volumes, costs per click (CPC), and competition levels for different keyword categories. The document finds weak or no correlations between certain metrics like search volume and CPC or competition levels. It advocates grouping keywords by categories like "long tail," "value," or "economy" based on search volume and CPC. The optimal keyword selection depends on marketing objectives like generating leads or brand awareness. Data is plotted to demonstrate budget allocation across different keyword groups.