Rules is a very nice module with a user-friendly interface which you can set some simple workflow in Drupal.

Install the following 2 features in Rules.

 

After installation, you can find a new the Rules panel in the Admin menu.

 

Let’s create a new Triggered rule which is fired when a new user is created.

 

Forget about the condition as we want to run the action whenever a new user is created. we proceed the setup by creating a Log to watchdog action.

 

Our Trigger rule will look like this. You can add more actions like email notification if you want.

 

Let’s check the watchdog after a new user is created.

 

Done =)

Reference: Drupal Module – Rules