In the Qur’an, Almighty Allah teaches us: “Ask Allah of His bounty. Lo! Allah is ever Knower of all things.” (An-Nisa’: 32) Also: “ And when My servant question thee concerning Me, then surely I am nigh. I answer the prayer of the suppliant when he crieth unto Me. So let them bear My call and let them trust in Me, in order that they may be led aright.” (Al-Baqarah: 186)

Mentioning the etiquettes of the du`aa, Muslim scholars state that the voice of the suppliant should be neither so loud nor so low. It is also part of the Sunnah to repeat the supplications three times, if you can. If not, one time will be sufficient, in sha’ Allah.
May Allah accept our supplications and grant us the best of deeds in this world and the best reward in the Hereafter, Aameen.