In the Qur'an Allah speaks of himself as “I” and “We”. In both cases there is a special meaning to it. In arabic it is possible to speak of one person in the plural as well as to speak of many persons in the singular. When is Allah speaking of himself as “I” and when as “We”?

“I” and 'Me'

Allah is speaking of himself as I, when He wants to point out his oneness which is the essence of His attributes. For a muslim there is nothing more important than accepting the oneness of the creator. Here is a verse where “I” and "Me" is used:

وَإِذَا سَأَلَكَ عِبَادِي عَنِّي فَإِنِّي قَرِيبٌ ۖ أُجِيبُ دَعْوَةَ الدَّاعِ إِذَا دَعَانِ ۖ فَلْيَسْتَجِيبُوا لِي وَلْيُؤْمِنُوا بِي لَعَلَّهُمْ يَرْشُدُونَ -

And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided. (Surah al-Baqara, 186)

إِنَّنِي أَنَا اللَّهُ لَا إِلَٰهَ إِلَّا أَنَا فَاعْبُدْنِي وَأَقِمِ الصَّلَاةَ لِذِكْرِي - 20:14

Indeed, I am Allah . There is no deity except Me, so worship Me and establish prayer for My remembrance

In this verse Allah uses “I” for himself to show first and foremost that He is the ONLY ONE that should be worshipped and supplicated. A muslim can never supplicate to another human. The only one we can supplicate to is Allah. That’s why he says “Me”. Moreover he uses “Me” to show that He is near to his servant. There is nothing between Allah and his creation, whenever we need Him, He will be near to us.

When Allah uses “We” for himself that shows His greatness and His majesty. It’s called “pluralis majestaetis”. The word “We” is used when Allah talks about something important and majestic. Here an example from the quran:

إِنَّا نَحْنُ نَزَّلْنَا الذِّكْرَ وَإِنَّا لَهُ لَحَافِظُونَ -

Indeed, it is We who sent down the Qur'an and indeed, We will be its guardian. (Surah al-Hijr, 9)

إِنَّا نَحْنُ نُحْيِي الْمَوْتَىٰ وَنَكْتُبُ مَا قَدَّمُوا وَآثَارَهُمْ ۚ وَكُلَّ شَيْءٍ أَحْصَيْنَاهُ فِي إِمَامٍ مُّبِينٍ -

"Indeed, it is We who bring the dead to life and record what they have put forth and what they left behind, and all things We have enumerated in a clear register. (Qur'an 36: 12)

To underline that importance Allah speaks of Himself as “We” and shows His Majesty and Power. It also also implies some work done by the angels. For example with respect to “Indeed, it is We who sent down the Qur'an and indeed, We will be its guardian.”, Angel Gabriel is the Carrier of the Revelation. ' We' describe Allah’s sovereignty over the worlds and His kingdom also denotes the control of Allah over everything in the universe that He has alone created, doesn't need any "Partner or Intercessor".