Shakespeare uses many poetic techniques, but here are some powerful ones.
Alliteration and Antithesis
Alliteration is repeated initial sounds, and it can be used to draw emphasis to something or make it more memorable, like a catchy slogan. Consider the witches’ line in the opening scene.
Fair is foul, and foul is fair.
Hover through the fog and filthy air. (enotes etext pdf p. 8)
In this case, there is alliteration of the “f” sound, which makes the witches seem even more eerie. It also gives the witches’ lines a spell-like quality.
In these same lines there is also antithesis, or contrast. You can read more about antithesis here (http://www.enotes.com/topic/Antithesis). Basically, by contrasting “fair” and “foul,” the witches set up one of the main themes of Macbeth: things are not always what they seem, and sometimes something can be two things at once. This is also foreshadowing of Macbeth’s descent into evil.
Another common poetic technique in Macbeth is rhyme. This makes the witches’ chanting both more interesting and more frightening.
Round about the cauldron go:
In the poison'd entrails throw.(5)
Toad, that under cold stone
Days and nights has thirty-one
Swelter'd venom sleeping got,
Boil thou first i’ the charmed pot. (Act IV, Scene 1, p. 57.
The rhyme gives the lines a chanting, sing-song quality. The constant barrage of body parts sounds better with rhyme. It makes the witches mysterious and frightening, and contributes to the other-worldly quality they have that is so important.
Simile and Metaphor
Shakespeare will always have its fair share of simile and metaphor, but some if the nicest ones are in Macbeth!
Consider the description of Macbeth’s battle in Act I.
As two spent swimmers that do cling together(10)
And choke their art. (Act I, Scene 2, p. 9)
What a simile! This indirect comparison, using “as” to compare the fighters to swimmers, is very vivid. Another good one is one of Lady Macbeth’s more famous lines.
Yet do I fear thy nature;
It is too full o’ the milk of human kindness(15)
To catch the nearest way. (Act I, Scene 5, p. 19)
This metaphor really captures both Lady Macbeth’s twisted thinking and the irony in milk flowing where blood actually is to flow later. She does not need to worry about her husband being too kind!
For more on wordplay, read here: http://www.enotes.com/macbeth/reading-shakespeare#wordplay
To read more about style in Macbeth, see here:
Shakespeare, William. "Macbeth." Enotes.com. Enotes.com. Web. 08 May 2012. <http://www.enotes.com/macbeth-text>.