In an interesting post, John Ellis points out the "Seven Habits Of Highly Effective Pay-Per-Click Advertisers".

A brief introduction to the Seven Ways to score include:

• Separate Content from Search: "The separation provides much more insight into what is working, and more importantly what is not working."
• Control spending by adjusting bid amounts, not daily spend budget
• Create a negative keyword list
• Conversion matters, not click-through rate (CTR)
• Avoid #1
• Bid Exact, Avoid Broad
• Good Analytics

Guidelines may differ from advertiser to advertiser. However, this gives a clear headstart to effective PPC advertising.