A lot of background knowledge is required for writing good Drupal code. Of course, the aim of a book such as this is to try to provide as much of that background knowledge as possible. However, self-documentation and research still remain key, and there are a number of resources that a Drupal developer should have on-hand.
The first is the official online API documentation. Just about every function in Drupal is documented using in-line code documentation. The Doxygen program is then used to extract that documentation and format it. You can access the full API documentation online at http://api.drupal.org.
Along with using the Drupal APIs, we strive to comply with Drupal's coding conventions. Best practices ...