Du`aa’ is the essence of worship, as the Prophet (peace and blessings be upon him) stated in one of his hadiths. Almighty Allah teaches us to call upon Him and seek His forgiveness all the time.
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)
Du`aa’ should be by Allah’s Names and Attributes that are based on the Qur’an or authentic Hadith. Allah’s Names and Attributes are divine-based, so no one can invent a name and attribute it to Allah Almighy. Allah says: “And (all) the Most Beautiful Names belong to Allah, so call on Him by them…” (Al-A`raf: 180)
Therefore, stick to calling Allah by His Names and Attributes which are mentioned in the Qur’an or the authentic Sunnah.