Look towards the sky and recite:
أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ وَأَشْهَدُ أَنَّ مُحَمَّدَاً
عَبْدَهُ وَرَسُولَهُ
Ash-hadu an laa ilaha illa Allahu wahdahu laa shareeka lahu wa ash-hadu anna Muhammadan ‘abduhu wa rasuluh!
“I testify that there is no one worthy of worship besides Allah. He is all by Himself and has no partner and I testify that Muhammad is Allah’s Rasul (Messenger)”.
Eight doors of Jannah will be open for the reciter of this dua. He will be able to enter from whichever door he pleases. (Mishkat)
It is recorded in the same narration that the dua should be recited three times. (Hisnul Hasin)
There after this du’a should be recited
اللَّهُمَّ اجْعَلْنِي مِنَ التَّوَّابِينَ وَاجْعَلْنِي مِنَ الْمُتَطَهِّرِينَ
Allahumma-j’alnee min-al-tawwaabeena wa-j’alnee min-al-mutatahireen!
“O Allah, count me (make me) among those who seek forgiveness and amongst those who stay clean”. (Hisnul Hasin)
Also recite this dua
سُبْحَانَكَ اللَّهُمَّ وَبِحَمْدِكَ أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا أَنْتَ أَسْتَغْفِرُكَ وَأَتُوبَ إِلَيْكَ
Subhanaka Allahumma wa bi-hamdika ash-hadu an laa ilaaha illaa anta astaghfiruka wa atubu ilayka!
“O Allah, You are pure, I praise You and testify that only You are worthy of worship and I seek forgiveness from You (I turn to You for forgiveness).
(Hisnul Hasin, from Mustadrak)