I had a chance to write a guest post for Web Analytics World last week. In it I talked about quickly diagnosing quick jumps or dips in traffic or conversions, and oulined three steps for getting to the bottom of a shift in traffic:

1. Consider the Source
2. Analyze Your Overall Mix
3. Identify Who or What is Sending You Traffic

To learn more about each step and how you can accomplish the above in Google Analytics, check out the post.