We have a new course at school this year, Design Patterns & Frameworks
I’ve been coding OO code for about 2 years now and I’ve been using some patterns without knowing it.
We had to buy the book Head First Design Patterns, just finished the book yesterday 
a 600+ pages book.
I enjoyed reading the book from the moment I opened it, it’s such a easy way to learn about patterns. Examples, crossword puzzles,…
If you want to enhance your OO skills I really recommend reading this book.
(Examples are all in java but you can also download the C# code on their website)