My Lord, Expand My Chest
رَبِّ اشْرَحْ لِي صَدْرِي وَيَسِّرْ لِي أَمْرِي وَاحْلُلْ عُقْدَةً مِنْ لِسَانِي يَفْقَهُوا قَوْلِي
Rabbish-rah li sadri wa yassir li amri wahlul 'uqdatan min lisani yafqahu qawli.
My Lord, expand my chest for me, make my task easy for me, and untie the knot in my tongue so that they may understand what I say.
What it means
Musa said this when he was told to go and speak to Pharaoh. He did not ask for the task to be removed, only for the courage, the ease and the words to carry it out. That makes it the dua for anything you have to face and would rather avoid.
When and how
Say it before an exam, a difficult conversation, a presentation, or any moment where you have to speak and your nerve is failing.
Its virtue
It is the supplication Allah records from Musa in Surah Taha, and the same surah reports Allah's answer: you have been granted your request.
Source
Quran 20:25-28
Quranic text from Tanzil.net, Creative Commons Attribution 3.0.