they are 3 standard design pattern for android developer that newst of them (and better than in my opinion !! ) is MVVM (Model View ViewModel) here is the very simple example of this design pattern for user login and register
for read more about android design patterns , isuggest you to read this article
in this sample i use MVVM design pattern and very good plugin and framework ! that speeded up my coding very much , so i suggest you to use it too.
at first read this article for know more about MVVM design pattern and how this framework made and also install the plugin based on the tutorial in your android studio