Learn how to use the Rules core module. It is one of the best things about Drupal 7. To me, it ranks up there with Views and Panels. I’m really annoyed with myself for taking so long to get the the power of this really nifty feature.
Watch this series from the wonderful folk at Nodeone. This really helped me.
Next, I’ll post on how I used Rules to autotag forum posts with the location, the state of residence specified on the user’s account.