In my opinion, it's crucial to gain a deeper understanding of the following topics:
1) Difference between call by value and call by reference in JavaScript
Importance: With AngularJS heavily relying on objects, grasping this concept will clarify their behavior.
2) Scope chain and IIFE (Immediately Invocable Function Expression)
Importance: IIFEs play a significant role in manipulating scope when developing applications with AngularJS.
3) Closures
Importance: Closures are fundamental in JavaScript and widely used in popular libraries and frameworks. Understanding closures will also give insight into how factories operate.
4) Dependency Injection
Importance: This JavaScript concept is foundational to AngularJS.
5) It's beneficial to review some well-regarded style guides for AngularJS. One example is the following: https://github.com/johnpapa/angular-styleguide