If you're looking for advice on how to maximise the effectiveness of your Google Adwords campaign, then you will find this PDF from the Google team - The Maximum Effect - very useful. Google has compiled a 41-page document offering the best tips on Google Adwords after having studied thousands of Adwords campaigns. Here's a taste of what can be found within it:
Chapter 1 – Setting Goals
Chapter 2 – Selecting Keywords (A four-step process)
Chapter 3 – Developing Ads
Chapter 5 – Tracking Results
Chapter 6 – Optimizing Again
An essential guide for those new to Adwords and an interesting read for those who already have experience with Adwords.
Google Adwords - useful tutorials