It is such a simple thing but it can be the most difficult thing to do.
The "thing" that I meant was just "throw your garbage, litter, trash, or whatever name you give to unused things to the place where the things belong, trash bin or dust bin".
Make a habit to dump your waste in the right place. That will show your intention to join the troop of environment friendly legions. Besides, it will ease garbage collector life.
Unfortunately, millions of Indonesians seem have difficulties to adopt this simplest way. Probably, I am wrong, it may be the most difficult thing to do, more difficult than attending a seminar of green lifestyle.