Welcome to the Android Development world 😄. Are you using Kotlin or Java? If you started with Java, it's a great way to start! But I will suggest you learn Kotlin too. You probably want to check these topics, since I don't know what do you mean by basics you can remove from the list what you already know.

• Network calls with Retrofit.
• OkHttp interceptors.
• Storing information in the database.
• Android Architecture Components (Room, Livedata, Navigation, WorkManager...)
• Notifications
• Services
• Firebase (Authentication using Firebase, Notifications with Firebase, Storing data using Firebase, DynamicLinks).
• Build Variants.
• Proguard.
• Testing with Espresso.
• Animations.

Good topics to read even if there are not specifically for Android:

• Solid Principles.
• Clean Architecture.
• Reactive Programming.
• Dependency injection.
• TDD (Test Driven Development).

There are a lot of things to learn! So do it at your own pace 😄.

Resources

Android Development course with Kotlin in Udacity

Android Codelabs