I prefer to organize my source code based on recommended Android app architecture, which is also known as MVVM architecture.

Image source: MindOrks

This is what my package/folder structure looks like in Java root folder.

This works for a small app, which is exactly what I’m doing now. However, I imagine if your app is huge and contributed by many developers, you may want to break it down into different modules/features instead.

Module1
└─── ui
└─── viewmodel
└─── repository
└─── local
└─── remote
    ...
Module2
└─── ui
└─── viewmodel
└─── repository
└─── local
└─── remote
    ...
...

This allows your modules to be exported or shared as generic libraries easily in the future. Since my app is small, I'm good with what I'm doing now.

[Updated - July 02, 2022]: Given that I now have a bit of experience. This is my current package naming convention based on the latest app architecture guide.

root package
└─── data
     └─── local
     └─── mapper
     └─── remote
     └─── repository
└─── domain
     └─── model
     └─── repository
└─── ui
     └─── screens
     └─── theme
     └─── viewmodel
└─── utils

• mapper contains extension functions to convert data to and from different layers.

For app reference, you can refer here.