Top 20 mistakes you will make on your 1st Drupal project
This is a great article / presentation by Iztok Smolič on slideshare.net about the top 20 mistakes that one will make on their first Drupal project. Luckily for me I had a pretty good teacher who taught me the basic, even if at the time he wasn't able to fully explain the reasoning behind why - e.g. Hacking Core / Contrib Modules (slide 22). At the time, he was very adamant that the very last thing we ever wanted to do was change code. Learning on the job and with a glooming deadline over our heads somethings were just taken at face value and not fully explained the reasoning behind it but the results was that I would look for another way to fix the issue like using hooks if the code has to be modified.
