Hadhrat Mu'aadh bin Jabal (may Allaah be pleased with him) relates that someone once asked Rasulullaah (peace be upon him) what the highest level of Imaan was (and with which actions can it be reached).
Rasulullaah (peace be upon him) told him that it will be reached when a person loves others for the sake of Allaah and dislikes them for the sake of Allaah ( meaning that one makes friends and enemies only to please Allaah).
The second thing Rasulullaah (peace be upon him) mentioned was that a person uses his tongue for the Dhikr (remembrance) of Allaah.
Hadhrat Mu'aadh (may Allaah be pleased with him) then asked Rasulullaah (peace be upon him) to mention more such actions.
Rasulullaah (peace be upon him) said that another such action is to like for others what you like for yourself and to dislike for others what you dislike for yourself.
We must also make an effort to make our hearts such that we want only good for everyone. Instead of telling our brothers and sisters useless jokes and stories, we should rather say Allaahu Akbar (Allaah is The Greatest) or Subhaanallaah (Glory be to Allaah) or some other Dhikr.
Just as we like our school bag and books to be clean and neat, we must not damage the bags and books of others and when we borrow something from anyone, we must make sure that we look after it and return it just as it was when they lent it to us.