Bringing happiness to a Muslim is a Sunnah and an act of great merit. There are many ways in which this can be achieved. Many people find themselves in distress and difficulty. By cheering someone up, it lightens their difficulty and gives hope.
This little act of goodness could be a means of someone changing their life. This could be achieved by speaking in a polite manner, an invitation to a meal or presenting a gift, etc. Any action of this nature would entitle one to great benefits which are found in the Ahadith
Hazrat Umar t narrates from Rasulullah (Sallallahu Alaihi Wasallam), “The best action is to bring happiness to a fellow Muslim, either by concealing his faults, satiating his hunger or fulfilling his need.” (Al Mu'jamul Awsat lit Tabrani)
Hazrat Anas (R) narrates that Nabi (Sallallahu Alaihi Wasallam) said: “Whoever meets his Muslim brother and makes him happy with something that Allah likes, Allah will make him happy on the Day of Qiyamah.” (Al Mu'jamus Saghir lit Tabrani)
Hazrat Hasan bin Ali (R) narrates that Nabi (Sallallahu Alaihi Wasallam) said, “Bringing happiness to a fellow Muslim is one of those actions which make the forgiveness of Allah binding upon a person.” (Al Mu'jamul Kabir wal Awsat lit Tabrani)
Hazrat Ibn Abbas (R) narrates that Rasulullah (Sallallahu Alaihi Wasallam) said, “Verily the most beloved of actions to Allah after the Fardh duties is bringing happiness to a fellow Muslim.” (Al Mu'jamul Kabir wal Awsat lit Tabrani)