رَبِّ اشْرَحْ لِي صَدْرِي وَيَسِّرْ لِي أَمْرِي وَاحْلُلْ عُقْدَةً مِنْ لِسَانِي يَفْقَهُوا قَوْلِي

Rabb-ishrah li sadri, wa yassir li ‘amri, Wah-lul ‘uqdatam-min-li-saani, Yaf-qahuu qawlii

O my Lord! Open for me my chest (grant me self-confidence, contentment, and boldness); Ease my task for me; And remove the impediment from my speech, so they may understand what I say
[Surah Ta-Ha; 20:25-28]
A du’a that Musa (alayhis salam) made when proceeding to the court of Fir’awn (Pharoah) for the arguments (inviting him to Islam)

اَللَّهُمَّ إِنِّي أَسْأَلُكَ عِلْمًا نَافِعًا , وَ رِزْقًا طَيَّبًا , وَ عَمَلاً مُتَقَبَّلاً

Allahumma inni as’aluka ‘Ilman naafi’an, wa rizqan tayyiban, wa ‘amalan mutaqabbalan

O Allah! I ask You for knowledge that is of benefit, a good provision and deeds that will be accepted.
[Ibn Majah and others]

 
اللِّهُم انّفَعنِي بِمَا عَلَّمتَنِي وَ عَلِّمنِيِ مَا يَنفَعنِي

اللَّهُمَّ الْطُفْ بِىْ فِىْ تَيْسِيْرِ كُلِّ عَسِيْرٍ فَاِنَّ تَيْسِيْرَكُلِّ عَسِيْرٍ عَلَيْكَ يَسِيْرٌَ

Allahumma Oltuf bi fi taysiri kulli ‘aseer, fainna taysirra kuuli ‘aseerin ‘alaika yasser

O Allah!  Make easy for me every difficult thing, with Your special favor and Kindness, for it is easy for You to make every difficult thing easy