Angels are always in God's immediate presence

Luke 12 8, 9 I tell you, whoever publicly acknowledges me before others, the Son of Man will also acknowledge before the angels of God. But whoever disowns me before others will be disowned before the angels of God.

Here the repeated phrase before the angels of God is another way of speaking of the immediate presence of God (see the parallel in Matthew 10:32, 33). We learn, therefore, with regard to angels, that they are always in God's immediate presence. What we also learn, however, is that believers ought to always be aware of an invisible world, the world of angels that is the world that really counts. So often we are aware of what men see and what they think but more important is what the angels see and what they think. When tempted to deny the Lord, think of the angels.
Revelation 3:5 is parallel in part
The one who is victorious will ... be dressed in white. I will never blot out the name of that person from the book of life, but will acknowledge that name before my Father and his angels.Also relevant is Luke 15:10, which we tend to think of as referring to angels but is really referring to God himself
In the same way, I tell you, there is rejoicing in the presence of the angels of God over one sinner who repents.
In Luke 1:19 Gabriel reveals that he stands always in the presence of God.

Angels are just, good, wise and discerning

2 Samuel 14:17, 20 “And now your servant says, ‘May the word of my lord the king secure my inheritance, for my lord the king is like an angel of God in discerning good and evil. May the LORD your God be with you.’ ” ... "Your servant Joab did this to change the present situation. My lord has wisdom like that of an angel of God--he knows everything that happens in the land."

(Also see 19:27 And he has slandered your servant to my lord the king. My lord the king is like an angel of God; so do whatever you wish.) 

These words spoken by the wise woman of Tekoa in two instances are really asides and we should be careful not to make too much of them. They do appear, however, to recognise a wisdom and discernment in the minds of angels that is beyond what we ordinarily find among men. Justice and goodness are also implied. These creatures are highly intelligent and they have not only a mental dexterity but also a moral integrity that remains untouched by sin. This enables them to know good from evil with great insight.

Angels do not marry or have sexual relations

Matthew 22:30 At the resurrection people will neither marry nor be given in marriage; they will be like the angels in heaven.

When Jesus says that at the resurrection, people will be like the angels, he cannot mean in every respect. He is narrowing down to the fact that they will not marry (or have sexual relations, presumably) which, far from being bad news, means that they will become like the angels who, being spiritual creatures, do not marry (or engage in sexual activity). Angels relate to one another as do brothers and sisters. This would seem to preclude the idea that the Nephilim of Genesis 6 were heavenly creatures rather than earthly. 

Angels are inferior to Christ but serve as God's messengers

Hebrews 1:4-7 So he became as much superior to the angels as the name he has inherited is superior to theirs. For to which of the angels did God ever say, ‘You are my Son; today I have become your Father’? Or again, ‘I will be his Father, and he will be my Son’? And again, when God brings his firstborn into the world, he says, ‘Let all God’s angels worship him.’ In speaking of the angels he says, ‘He makes his angels spirits, and his servants flames of fire.’ 

Christ's name is superior to that of the angles as although they are referred to as the sons of God at times, he alone is the Son of God. This is fitting because although he was made a little lower than the angels in the incarnation he became as much superior to the angels as the name he has inherited is superior to theirs. The very fact that all the angels worshipped the incarnate Son shows that he is God. (If all were worshipping the Son then none were doing anything else). Angels, in distinction from the Son of God, are like wind and thunder. They are messengers bringing God's message to earth. Like the wind they are invisible and like the lightning they are glorious. They are swift messengers from heaven.

Angels came and attended Jesus tempted in the wilderness

Matthew 4:11 Then the devil left him, and angels came and attended him.

Gill says that these angels came to Jesus in a visible, human form, as they were used to do under the Old Testament dispensation, which seems likely. It happened after the temptation was over; after Satan was foiled, and was gone. The timing shows that Christ alone had got the victory over him, without any help or assistance from the angels. Gill understands them as bringing him food of their own, as with Elijah, (1 Kings 19:5,-8) to satisfy his hunger and refresh him

Thus, says Gill, as the angels are ministering spirits to the heirs of salvation, both in a temporal and in a spiritual sense, (Hebrews 1:14 ) so they were to Christ. Nothing is more frequent with the Jews than to call the angels "ministering angels".

Spurgeon says that the enemy left him when he had shot his last bolt ... for a season .... So soon as the evil one had departed, angels appeared to fulfil a ministry for which they eagerly longed, but which the presence of the devil hindered. No doubt they had been hovering near, waiting their opportunity. These holy beings might not come upon the scene while the battle was being fought, lest they should seem to divide the honours of the day; but when the duel was ended, they hastened to bring food for the body and comfort for the mind of the champion King. It was a battle royal, and the victory deserved to be celebrated by the courtiers of the heavenly King. Let us behold, these angels, learn from their example, and believe that they are also near to all the warriors of the cross in their hour of conflict with the fiend. O Tempted but Triumphant King, thy servants worship thee, and ask permission and grace to minister to thee as angels did!

Mark 1:13 is parallel
and he was in the wilderness forty days, being tempted by Satan. He was with the wild animals, and angels attended him. 

Angels are very interested in gospel matters

1 Peter 1:12 It was revealed to them [the prophets] that they were not serving themselves but you, when they spoke of the things that have now been told you by those who have preached the gospel to you by the Holy Spirit sent from heaven. Even angels long to look into these things.

It is clear from Scripture that there is no salvation for fallen angels. They are very interested in anything to do with the salvation of human beings, nevertheless. They appear to be eager Bible students. It is not clear how Peter knows this.

Jamieson, Fausset and Brown say that these things are "the things now reported unto you" by the evangelistic preachers "Christ's sufferings and the glory that should follow" (1:11, 12 ). Tehy say that angels do not any more than ourselves possess an intuitive knowledge of redemption. "To look into" in Greek is literally, "to bend over so as to look deeply into and see to the bottom of a thing." As the cherubim stood bending over the mercy seat, the emblem of redemption, in the holiest place, so the angels intently gaze upon and desire to fathom the depths of "the great mystery of godliness, God manifest in the flesh, justified in the Spirit, seen of angels" (1 Timothy 3:16 ). Their "ministry to the heirs of salvation" naturally disposes them to wish to penetrate this mystery as reflecting such glory on the love, justice, wisdom, and power of their and our God and Lord. They can know it only through its manifestation in the Church, as they personally have not the direct share in it that we have. They quote Hofman in Alford, "Angels have only the contrast between good and evil, without the power of conversion from sin to righteousness: witnessing such conversion in the Church, they long to penetrate the knowledge of the means whereby it is brought about".

Angels will accompany Christ when he returns

Matthew 16:27 For the Son of Man is going to come in his Father’s glory with his angels, and then he will reward each person according to what they have done.

Mark 8:38 If anyone is ashamed of me and my words in this adulterous and sinful generation, the Son of Man will be ashamed of them when he comes in his Father’s glory with the holy angels.

Luke 9:26 Whoever is ashamed of me and my words, the Son of Man will be ashamed of them when he comes in his glory and in the glory of the Father and of the holy angels.

Matthew Poole says that Luke repeats the first two most perfectly, as here recorded. Mark expounds Luke’s words, where he saith that Christ shall come in his own glory, and in his Father’s and of the holy angels. By the glory of the holy angels is meant no more than attended by the holy angels, according to Matthew 13:41 and 1 Thessalonians 4:16 and other scriptures.

1 Thessalonians 4:16 says

For the Lord himself will come down

with a loud command,

with the voice of the archangel and

with the trumpet call of God,

and the dead in Christ will rise first.

There appears to be some parallelism here - the loud command is the voice of an archangel and can be pictured as the trumpet call of God. Christ calls the dead from their graves. He does so by sending his holy angels, led by the archangel, to gather the elect.

At the same time (Matthew 13:41) the angels will weed out all evil

The Son of Man will send out his angels, and they will weed out of his kingdom everything that causes sin and all who do evil.