An old but useful article about avoiding memory leaks on Android...

http://www.curious-creature.com/2008/12/18/avoid-memory-leaks-on-android/comment-page-1/

and a great link on mastering Android drawables:

https://skillsmatter.com/skillscasts/4619-mastering-android-drawables

https://speakerdeck.com/cyrilmottier/mastering-android-drawables