Housed in this repo is a wiki that goes over how to implement each of the 23 design patterns outlined in the book Design Patterns: Elements of Reusable Object-Oriented Software written by "The Gang of Four".
There is also some example code with comments showing you an example of each of the 23 design patterns in both Apex and JavaScript. Additionally (if you look in the wiki) there is a video tutorial where I write the code live with you while we go over each pattern.
If you believe there is any information missing from this guide or that it needs more info in certain places, please submit an issue on this repo here and I'll add it ASAP!
Aside from Design Patterns: Elements of Reusable Object-Oriented Software which you should absolutely read. There is also an excellent book focused on Design Patterns in Apex written by Jitendra Zaa and Anshul Verma titled Apex Design Patterns that I would recommend reading!