A common mistake for newcomers to PPC is to select very permissive keyword match types in an attempt to get the most traffic to their site. The whole point of doing PPC, they reason, is to generate traffic. So the more traffic I'm getting, the better my PPC is working, right?
Don't forget that you are not aiming for maximum traffic (per dollar of budget), you're aiming for maximum conversions (per dollar of budget). If you simply wanted to max out the traffic to your site you could run ads for some super-obscure (and non-competitive) keyword, and thousand of (confused) people would flood into your website before bouncing right out again.