Service is meant to change your view of others more than your view of yourself.

Here is video to use with young people that might encourage them beyond doing service just to feel better about themselves.

Philippians 2 reminds us

If there is any encouragement in Christ, any solace in love, any participation in the Spirit, any compassion and mercy, complete my joy by being of the same mind, with the same love, united in heart, thinking one thing. Do nothing out of selfishness or out of vainglory; rather, humbly regard others as more important than yourselves, each looking out not for his own interests, but [also] everyone for those of others. Have among yourselves the same attitude that is also yours in Christ Jesus