Regarding the topic we would like to quote Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, who stated:

The Qur’an, which is originally in Arabic, is revealed by Allah Almighty. Arabic is the mother tongue of Prophet Muhammad (peace and blessings be upon him). The Arabic language of the Qur’an has a unique rhetorical style that is the perfection of rhetoric and eloquence. Speaking of this, Allah Almighty says, “In plain Arabic speech.” (Ash-Shu`ara’ 26:195)

It has been customary among the native speakers of Arabic that in expressing oneself, one usually says ‘I’. However, in speaking as a member of a group, one says ‘We’. In Arabic, however, an individual may express himself while addressing a group of people, by saying ‘We’ as a sign of self-esteem.

It is worth noting that such methods of address (i.e. I and we), along with their different denotations are found in languages other than Arabic.”

There are many verses in the Qur’an where Allah expresses Himself by using the pronoun ‘We’. For example, Allah Almighty says, “Lo! We, even We, reveal the Reminder, and lo! We verily are its Guardian.” (Al-Hijr: 9)
In another occasion, Allah Almighty says: “Lo! We verily do help Our Messengers, and those who believe, in the life of the world and on the day when the witnesses arise.” (Ghafir: 51)
I think that when the true believer reads some verses of the Glorious Qur’an, which do address Allah by using the pronoun ‘We’, this will not shake his belief that Allah is One, and that He Almighty possesses certain sublime attributes that far exceed us mortals. Such attributes are capable of directing people’s attention to worshipping Allah, the One and the Sublime.”

Here, we’d like also to cite the words of Imam Ibn Taymiyah while addressing the same issue. He states: “The pronoun ‘We’ is commonly used by people especially kings and statesmen, when issuing official decrees. They usually say ‘We decide to do so and so’, while the person speaking or issuing the decree is one person, not a group.

It is worthy of stressing here that the one who deserves absolute glory and honor is Allah the Great. When Allah Almighty says ‘We’, then the word refers to the fact that He is Exalted and Glorified. The denotation of the word ‘We’ shouldn’t have any negative impact on a Muslim’s belief in the Oneness of Allah.
When a Muslim fails to understand the hidden meanings of certain Qur’anic verses and their contextual connotations, he should try to determine the meanings by referring to other verses whose meanings are easier to grasp. For example, when a Christian insists that Allah’s saying, “Lo! We, even We, reveal the Reminder, and lo! We verily are its Guardian”, is evidence of the Trinity, we can simply direct him to read other verses that reveal one clear meaning, such as “Say: He is Allah, the One! Allah, the eternally besought of all.” (Al-Ikhlas: 1-2)