What stylistic devices are used in Lady Macbeth's soliloquy in Act I, Scene 5?

In this soliloquy in Act I, Scene 5, Lady Macbeth establishes herself as incredibly ambitious, immoral, and cunning. Let's see which stylistic devices in particular help convey her villainous character during this soliloquy.

1. Apostrophe. While apostrophes are, of course, those little marks of punctuation, apostrophe is also a literary device in which the speaker addresses someone or something who isn't actually there. Keep in mind that Lady Macbeth is alone during this speech. She's holding the letter from her husband, and talking aloud to herself. When Lady Macbeth directs her comments toward her husband, calling him "thee" and "thou," she's using apostrophe. This stylistic device adds drama to the scene and probably helps the actress project her voice better, and turn her face more toward the audience, than if she were simply muttering to herself.

2. Metaphor. By saying her husband has too much "milk of human kindness," Lady Macbeth uses a metaphor to criticize her husband's kind nature as babyish or womanly.

3. Parallelism and alliteration: "What thou wouldst highly, That wouldst thou holily." With a repetitive, balanced sentence structure and a clever following of "highly" with "holily," Lady Macbeth is calling extra attention to the artfulness of the idea she's talking about here: that her husband really wants something, but he's too goody-goody to do what's necessary to get it.

4. Personification. By talking about the "valor" of her own tongue (the bravery of her words) and by saying that "fate and metaphysical aid" both want Macbeth to be crowned, Lady Macbeth is speaking in a firm, confident, forceful way, which shows us that she's not simply the masculine one in her marriage but also the more powerful one. 

Lady Macbeth's soliloquies are rich in stylistic devices like these, and I'm sure you can find more examples of them if you continue to examine the text closely. The four listed above strike me as the most effective ones in establishing Lady Macbeth's terrifying willingness to do anything necessary to grab power for herself and her husband.