Recite:
بِسْمِ اللَّهِ تَوَكَّلْتُ عَلَى اللَّهِ وَلَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللَّهِ
Bismillahi tawakkaltu ‘ala Allahi wa la hawla wa laa quwwata illa billah!
“I depart with Allah’s name, relying on Him. It is Allah who saves us from sins with His guidance (the ability to do so).” (Tirmidhi)
It is stated in the hadith that if a person recites the above dua and departs then there is an (unseen) proclamation that his/her need will be fullfilled and that he will be protected from any harm or injury. On hearing this dua, the Satan goes away from the place and refrains from troubling the reciting person. (Tirmidhi)
Also look towards the sky and recite:
اللَّهُمَّ إِنِّي أَعُوذُ بِكَ أَنْ أَضِلَّ أَوْ أُضَّلَّ أَوْ أَظْلِمَ أَوْ أُظْلَمَ أَوْ أَجْهَلَ أَوْ يُجْهَلَ عَلَىَّ
Allahumma inni a’udhu bika min an adilla aw udalla aw adhlima aw udhlama aw ajhila aw yujhala ‘alayya
“O Allah, I seek refuge in You from misleading or being misled or oppressing or being oppressed or from being ignorant or bearing the result of ignorance”.(Mishkat)