Five things at once, when you do not know where to start
The Prophet ﷺ taught this to a man who could not remember longer supplications.
اللَّهُمَّ اغْفِرْ لِي وَارْحَمْنِي وَاهْدِنِي وَعَافِنِي وَارْزُقْنِي
Allāhumma-ghfir lī wa-rḥamnī wa-hdinī wa ʿāfinī wa-rzuqnī.
“O Allah, forgive me, have mercy on me, guide me, keep me well, and provide for me.”
The Prophet ﷺ said these five gather together your whole life, this one and the next.
The full narration
Abu Malik reported on the authority of his father that when a person embraced Islam, Allah's Messenger (ﷺ) used to teach him how to observe prayer and then commanded him to supplicate in these words:" O Allah, grant me pardon, have mercy upon me, direct me to the path of righteousness, grant me protection and provide me sustenance
Source
Ṣaḥīḥ Muslim · 6850
Ṣaḥīḥ
- Agreed upon as authentic (al-Bukhārī / Muslim)