I'm a big proponent of launching large pay-per-click campaigns, watching early results, and then honing, tweaking, refining.  I'm also a fan of "long tail" keywords (multiple words, more narrow and descriptive).  Unfortunately, Google AdWords doesn't always like long tail keywords due to their low search volumes.  My theory is that they use up more of Google's server space and resources than Google thinks they're worth.

It's critical to keep a close eye on your PPC campaign and pause or remove any keywords or ad groups that are performing poorly.  Specifically, if there's a low quality score, first try to solve it by (a) ensuring there's a close fit between the keyword, the ad copy and the landing page copy, and (b) writing a compelling ad that garners a good click-through rate.

If that doesn't work, pause or delete the keyword or ad group, no matter how much it hurts.  Believe it or not, a low quality score in one part of your campaign can drag down the performance of your entire campaign.  Unfair, you say?  I totally agree.  But it's Google's world - we just advertise in it.

Plenty more details about this, including tips to deal with it, are in my article "Rage Against the Machine - Tail Terms on Google AdWords."