1) use proguard  : set minifyEnabled true
    2) Remove unused resources : set shrinkResources true
    3) Remove everything that you are not using
    4) If you are using librarires ,try finding the snippet that you are really using,if you dont find any such version,try fiddling with the required class directly in your app instead of importing whole library
    5) Use vector drawable instead of pngs for your small icons and drawables
    6) Reduce png images clarity to point where it have same effect to human eye ,while its size is reduced heavily
    7) Try generating resources or draws on runtime instead of storing it before hand