Model, Practice, Notice, Reinforce
Developing good character may not come naturally to some because what some kiddos may not realize the intrinsic value.
I start with a read aloud. Each Kindess by Jacqueline Woodson, Mr. Peabody's Apples by Madonna, The Empty Pot by Demi are some that come to mind. There is also an open ended book, What should Danny Do? (the power to choose series)
Some time to discuss (morning meeting or closing meeting). Practice the skill.
Reinforcers could be verbal recognition of the deed, Dojo points, note home, stickers, or whatever else fits in with your classroom economy.
Vary the reinforcers to help kids transition from tangible rewards.