As far as I am aware there are 3 interpretations of the usage of "We" in the Qur'an. One can understand all 3 meanings at once for every usage of "We". Indeed, every single ayah verse of the Qur'an is like an ocean of infinitely many guiding meanings. No verse can be reduced to a single meaning or interpretation. May Allah the Hadi, guide us to the Truth. Here I will try to explain the 3 interpretations I know, as I understand them:
1) Majestic "We" : Humans who think they can be kings and sultans to other humans, will often use this majestic "we" when referring to themselves. However, as stated in the Qur'an in Surah Nas, God is "Malik an-nas" "King of humans" ("the Sovereign of men"). Therefore such majestic titles and language will only properly befit our Creator, Allah and not any human or other creation. All creation is equal before its Creator. So the usage of "We" in the Qur'an, reminds us that Majesty and Glory belongs to none but God.
2) "Allah" is considered to be the name of God which encompasses all of Asma al-Husna (Beautiful Divine Attributes, Names of God), so when we say "Allah" it means: the Merciful, the Compassionate, the Just, the Creator, the Beautiful, the Loving, etc... So "We" could refer to "Allah" with the inference that all attributes we observe in creation, humans or nature, are the reflections of all the infinitely many Divine Attributes of God. (There are 99 names mentioned in the Qur'an but many more in hadiths.) This means: the beauty of the rose or the sunset or the birds or stars or women or galaxies are all various reflections of the same Infinite Divine Beauty. The mercy of all mother animals and human mothers is the reflection of the Infinite Divine Compassion. So the usage of "We" in the Qur'an, reminds us that all these attributes we observe in the Universe actually belong to the One God.
For more explanation on understanding creation as a reflection of Divine Names: http://pan-cck.blogspot.com/2013/07/does-praying-to-god-mean-we-should-not.html
3) "We" refers to God and the angels. Every particle, every atom, every light photon is created with an accompanying angel. In fact, particle physicists would know this better, what we call atoms and particles is not much more than the energy the motion of them. Looking inside the atom scientist find a ton of empty space and not much "matter", we know it is all motion and energy. This "energy" concept is similar to the concept of "angel"s. Just like humans can't exist without body or soul, nothing can exist without both matter and spirit, ie. angels. Imagine that our cells are "brought to life" through the millions of angels each cell carries. When we pray for health, the angels of our cells all say "Amin!" and Allah restores our cells responding to this chorus of prayers. This is how I understand the way God responds to our prayers in physical and other ways. As the Qur'an says:
****17:44 (Asad) The seven heavens  extol His limitless glory, and the earth, and all that they contain; and there is not a single thing but extols His limitless glory and praise: but you [O men] fail to grasp the manner of their glorifying Him!  Verily, He is forbearing, much-forgiving! -*****
I understand this to mean: everything glorifies and praises their Creator with their accompanying angels.
***8:9 (Asad) Lo! You were praying unto your Sustainer for aid, whereupon He thus responded to you: "I shall, verily, aid you with a thousand angels following one upon' another!" ***
Our prayers are responded to with angels.
***13:13 (Asad) and the thunder extols His limitless glory and praises Him, and [so do] the angels, in awe of Him;****
The thunder and the angels of the thunder praise God together.
***33:43 (Asad) He it is who bestows His blessings upon you, with His angels [echoing Him], so that He might take you out of the depths of darkness into the light. And, indeed, a dispenser of grace is He unto the believers. ***
All blessings, and since every created thing is a blessing of God, all creation is bestowed upon us with angels. Understanding that every thing is a blessing of God accompanied by angels will inshaAllah take us from darkness of the spirit to light, peace and security, salaam, inshaAllah.
***Qatadah reported from Anas ibn Malik (may Allah be pleased with him) who said: Allah's Messenger (peace and blessings be upon him) said, "Uhud is a mountain which loves us and which we love."****
Just like when we love a person it is their lively soul we love and not their dead bodies, when we love mountain Uhud, it is the angels of the mountain which we love and it is the angels of the mountain Uhud which loves us back. This is my interpretation, wAllahu a'lamu kulli shay' (verily God knows all) and may God forgive me for my mistakes.
You can also read this for more detail on this topic: http://pan-cck.blogspot.com/2012/10/khutbah-nature-and-hierarchy-of-life.html
When "We" refers to God and angels, it reminds us that there is nothing on Earth or in the Heavens that is created without an angel, it reminds us of the spiritual aspect of the Universe. It reminds us that just like the two sides of the coin cannot be separated from each other, the matter and the spirit, the atoms and the angels, the body and the soul, the creation and the reflections of the Divine Names, cannot be separated from each other, they exist together. It is a reminder of the Shariat-ulllah, the Divine Laws, the ways in which God creates and governs the Universe. In fact, understanding physics concepts such as "force" or "energy" becomes much easier when one interprets these concepts as the interaction of angels obeying the Divine Laws.
InshaAllah I pray this helps. May Allah allow us all to have "fiqh", the correct understanding and interpretation of the Qur'an. Allahumma arinal Haqqa Haqqan, warzuqna ittiba', wa arinal batila batilan, warzuqna ijtinabah. (May Allah allow us to see the Truth as the Truth and abide and live by it and to see the false as the false and allow us to avoid it), inshaAllah.
This could be used as khutbah/speech material.