First learn the basics, than apply these into learning more advance concepts.
Learn the each concept coming in your way, so when needed, it can be used in further studies, it help you making advancement.
Following are some of my questions, that are being arising through my mind and while started to learn to code the Android mobile apps development.
1- How to program core features and Classes in Java Programming language that are used in Android App Development.
2- What are the Key Java Programming language feature that are used in flow of  Android Mobile App Development.
- Java Looping Constructs
 - How to use Structured Data, Array
 - Common classes in Java Collection Frame Work
 - Array List
 - Hash maps
 - Group related Operations
 - Data into classes and interfaces
 - Java Primitive and user defined types
 - Fields
 - Methods
 - Generic parameters
 - Exception
 
3- How to customize the behavior of existing classes through the inheritance and polymorphism.
- sub classes
 - Overriding virtual methods
 
4- what are the core android components
- UI Elements
 - Activities
 
5- What is Android Studio and How it is used as a tool to develop mobile Apps for android.