Virtues of making Duaa for the Ummat

 Ubaadah ibn Saamit Radhiyallahu anhu narrates that Rasulullaah Sallallahu alayhi wasallam said, ‘Whosoever seeks Allaah’s pardon on behalf of the believing men and women, in lieu of every single believing man and woman, Allaah Ta’ala shall write for him a separate reward. (Al-Mu’jamul-Kabeer of Tabaraani as quoted in Majmauz-Zawaaid)
 
Abu Darda Radhiyallahu anhu narrated, “I heard Rasulullaah Sallallahu alayhi wasallam saying, ‘Whoever seeks forgiveness for the believing men and women twenty-seven times (or twenty-five times,) he will be amongst those whose du’aas are accepted, and the people of the earth will be given sustenance through them.” (Al-Mu’jamul-Kabeer of Tabaraani as quoted in Majmauz-Zawaaid no. 17600) 

A simple du’aa which can be recited is the following,

اَللّهُمَّ اغْفِرْ لِيْ وَ لِلْمُؤمِنِيْنَ وَ الْمُؤمِنَاتِ وَ الْمُسْلِمِيْنَ وَ الْمُسْلِمَاتِ
O Allaah, forgive me and the believing men and women, and the subservient men and women.

 
Ma’roof Kharkhi Rahmatullahi alayh said, “He who supplicates 10 times the following du’aa daily for the ummah of Muhammad SallAllahualayhiwasallam, his name will be written in the register of the abdaal (a group of high-ranking awliyaa),

اَللهُمَّ ارْحَمْ أُمَّة مُحَمَّدٍ أَللهُمَّ أصْلِحْ أُمَّةَ مُحَمَّدٍ اللّهُمَّ فَرِّجْ عَنْ أُمَّةِ مُحَمَّدٍ (صلى الله عليه وسلم)

O Allaah! Have mercy on the ummah of Muhammad (sallAllahu alayhi wa sallam). O Allaah! Reform the ummah of Muhammad SallAllahu alayhi wasallam. O Allaah! Remove calamities from the ummah of Muhammad SallAllahu alayhi wasallam. (Hilyatul-Awliya vol. 8 page 366)