If you get an error trying to install your Unity build on Android saying App not installed, then you need to change your project's package name in the Player Settings. To do this, go to File > Build Settings > Player Settings... > Player > Other Settings and find the Identification section. Make sure Override Default Package Name is checked and then change the value of Package Name to something like com.example.mygame.
Additionally, you may want to change Install Location to Automatic.
From adb logcat you might see
TaskPersister: File error accessing recents directory (directory doesn't exist?).