Act 1, scene 5 of Shakespeare's Macbeth is Lady Macbeth's first appearance in the play, and it's notable that she first appears entirely alone. All of the major characters in Macbeth—King Duncan, Macbeth, Banquo, Malcolm, Macduff—first appear with other characters. Few major characters enter this late in Shakespeare's plays—an exception, Macduff, doesn't enter Macbeth until act 2, scene 1—and even fewer characters make their first entrance alone. Richard, Duke of Gloucester—not-so-coincidentally another villain—enters alone in act 1, scene 1 of Richard III.

Lady Macbeth enters the scene reading a letter from Macbeth about his meeting with the three witches in which they prophesize that he "shalt be King hereafter!" After a brief interruption by a messenger with information that King Duncan will soon arrive at her castle, Lady Macbeth gives her most striking speech in the play. She calls on evil spirits to remove her humanity from her so that she'll be able to murder Duncan without any pangs of conscience or any sense of regret or remorse.

Shakespeare usually has highborn characters communicate with one another in verse, rather than in prose, which Shakespeare assigns to lower-born characters. However, Macbeth, a Scottish noble, writes his letter to Lady Macbeth in prose.

This give a sense of Macbeth's role in the play up to this point—that of a soldier, albeit a general, in Duncan's army and therefore subservient to Duncan—and it shows a certain sense of urgency on Macbeth's part in conveying the information about the witches to Lady Macbeth as clearly and directly as possible. Macbeth writes in haste, and he's already on his way back to Lady Macbeth at his castle. He simply doesn't have time to convey his thoughts in proper, poetic, courtly form.

Lady Macbeth uses repetition to emphasize particular points in her speeches. Referring to Macbeth, she considers the possibility of his reluctance to kill Duncan.

LADY MACBETH. What thou wouldst highly,
That wouldst thou holily; wouldst not play false,
And yet wouldst wrongly win.
(act 1, scene 5, lines 17–19)

For extra emphasis, Lady Macbeth contrasts "highly" with "holily," uses the multiple alliteration within those two words, and also concludes the line with three-word alliteration, "wouldst wrongly win."

Lady Macbeth implores the evil spirits to "make thick [her] blood," and she calls on elements in nature, and the imagery they bring to mind, to hide her actions: "Come, thick night."

She instructs Macbeth "to beguile the time, / Look like the time," adding the assonance in "beguile" and "like," the alliteration of "Look like," and a simile, "Look like the time," for good measure.

LADY MACBETH. [L]ook like the innocent flower,
But be the serpent under't.
(act 1, scene 5, lines 70–71)

In this famous admonition to Macbeth, Shakespeare—through Lady Macbeth—employs similes, metaphors, alliteration, imagery, symbolism, diction, and irony, all in just two lines.

The first part of Lady Macbeth's instructions to Macbeth— "Look like the innocent flower"—is a simile, as well as a metaphor of Macbeth as an "innocent flower." She repeats the alliteration—"Look like"—that she used just two lines previous and adds the imagery of the flower. Lady Macbeth wants Macbeth to appear as innocent and harmless as a flower to Duncan and those around him so that no one suspects his intentions towards Duncan and the throne.

The second half of Lady Macbeth's admonition to Macbeth is also a simile, a metaphor of Macbeth as a "serpent," contains alliteration—"But be"—and adds the imagery of the serpent. Shakespeare's diction, his word choice of "serpent" rather than "snake," emphasizes Macbeth's evil intentions.

With his use of "serpent," Shakespeare compares the symbolism of the common negative perception of a serpent with the pure evil and treachery of the serpent in the biblical story of Adam and Eve in the Garden of Eden.

The irony of these lines is that in instructing her husband to be a "snake in the grass" with regard to Duncan and his aspiration to the throne of Scotland, it is actually Lady Macbeth who takes the role of the serpent in the Garden of Eden, who tempts Macbeth not with great knowledge but with great power.

The literary devices that William Shakespeare uses in Macbeth act 1, scene 5, include metaphor, alliteration, and apostrophe. The combination of parallel structure and several types of repetition is also effectively deployed.

Metaphor is direct comparison of two apparently unlike things for effect. Lady Macbeth addresses her husband in absentia, describing his nature using a metaphor equating kindness with milk: "It is too full o' the milk of human kindness."

Alliteration, the repetition of initial consonant sounds, appears in numerous places: "you murdering ministers, / Wherever in your sightless substances."

When she summons up her courage and resolution to act boldly, she does so using by calling upon the spirits and to the night using apostrophe—direct address to a person, thing, or concept—"Come, you spirits/ That tend on mortal thoughts. . . . Come, thick night."

Parallel structure is the use of the same syntax or grammatical construction. Repetition of the same word, one type of which is anaphora (or a phrase: an epimone), is used here. These are combined in Lady Macbeth's exhortations to Macbeth about how to behave ("thou wouldst" or "thou wouldst not," "thou shouldst," and then contrasting "thou must" with the rhyming "thou dost"):

. . . thou wouldst be great;
Art not without ambition, but without
The illness should attend it: what thou wouldst highly,
That wouldst thou holily; wouldst not play false,
And yet wouldst wrongly win: thou'ldst have, great Glamis,
That which cries 'Thus thou must do, if thou have it;
And that which rather thou dost fear to do
Than wishest should be undone.

In this scene, Shakespeare uses a number of metaphors and similes. For example, Lady Macbeth says that she wants to "pour my spirits in thine ear," referring to her desire to fill her husband with evil thoughts, comparing them to spirits. Later, she says to Macbeth, "Your face, my thane, is as a book where men / May read strange matters." In this simile, she compares Macbeth's face to a book in which people can plainly read that he has strange thoughts. In other words, his face is far too open and can be read as easily as a book.

This scene also features personification. For example, Lady Macbeth says the following:

"Come, thick night,
And pall thee in the dunnest smoke of hell,
That my keen knife see not the wound it makes,
Nor heaven peep through the blanket of the dark
To cry 'Hold, hold!'"

In this passage, Lady Macbeth implores night to come to cloak her in smoke so that her knife will not see the wound it causes and that the heavens will not tell her to stop her murderous deeds. Both night and the heavens are personified, or made human.

There are also many examples of alliteration in this scene. For example, Lady Macbeth says, "Give solely sovereign sway and masterdom." Alliteration involves the repetition of initial sounds of words and makes the scene sound more poetic.

In Macbeth Act I, scene 5, Lady Macbeth greets her husband and receives his news that Duncan is on his way to their castle.

Lady Macbeth uses a strong combination of figurative language to capture her emotional response to her husband's news. 

Personification

Lady Macbeth uses personification in referring to "the raven himself is hoarse that croaks the fatal entrance of Duncan" (39-40).  Besides giving the raven given human qualities, Lady Macbeth also ascribes to him a prophetic voice; this type of bird was often thought to be a harbinger of doom.  She transfers her own feelings to the bird, such as her desire for Duncan's death. 

She employs personification again later in her speech with the wish that her "keen knife see not the wound it makes" (51).  Her thoughts are of murder. She gives human qualities to the murder weapon, but she is really speaking to herself in an attempt to stay her resolve to carry out the foul deed.

Metaphor

Lady Macbeth addresses her husband through the use of metaphor:

Your face, my Thane, is as a book where men
May read strange matters. (67-68)

As she greets her husband, she observes his expression, and compares the open honesty in his face to reading an open book.  Macbeth struggles to conceal his feelings.  Lady Macbeth feels she must correct this, especially with Duncan's impending arrival.  She suggests, using simile that Macbeth "look like th'innocent flower, but be the serpent under't" (64-65).  Her comparison suggests that Macbeth conceal his true purpose, like the serpent (Biblical allusion), and have all the charm of the flower to his guest.