I recommend reading "CodeIgniter Handbook Vol. 1: Who Needs Ruby?" to anybody who has just even tried using CodeIgniter! It's totally worth the $10 I spent on it!
This book will introduce and explain all the concepts of making your CodeIgniter usage much cleaner and easier to manage using DRY concepts. This book will explain how to use the author's code and why it works; something you don't get from just reading the code.
Even if you do not decide to use his code, the DRY concepts will open your eyes to implementing them into other projects.
You can buy the book online here: