The folks over at Kneoteric eSolutions have put together a pretty decent list of some common oversights that lead to paid campaign failures.
Some of the big ones mentioned:
Don't let my quick listing fool you. The author's listing goes into a great bit of detail. This also looks to be part of a pending two part series on the topic.
- Running a campaign on default settings
- Turning a blind eye to geo targeting
- Failing to bid on your brand name
27 oversights that lead to paid campaign downfall