How is ambition shown in drama Macbeth?

Ambition is the core theme of Macbeth, the driving force behind all the events of the play. When, in act 1, scene 3, the witches greet Macbeth as "thane of Cawdor," and tell him that he "shalt be king hereafter," this plants the first seed of ambition in Macbeth's mind. At first, Macbeth disbelieves the witches, but when Ross arrives to tell Macbeth that he has indeed been made thane of Cawdor, the impossible becomes possible for Macbeth. This is the beginning of his descent into wrongdoing, subsequent guilt, and madness.
The corrupting nature of ambition in this play also relies heavily upon the idea that the ambition of one person can feed upon that of another. While Macbeth is ambitious on his own account, at first, the thoughts which occur to him as regards becoming king seem "horrible imaginings," and he says, "If chance will have me king, why, chance may crown me, without my stir." That is, if his fate is to be king, then Macbeth will simply let it happen—although the idea appeals to him, Macbeth does not intend to do anything to further it.
It is Lady Macbeth who truly sets the events of the play in motion, turning ambition from a hope into an active pursuit. She fears that Macbeth is "too full o' the milk of human kindness," although "not without ambition." She determines that she will "chastise with the valour of my tongue / All that impedes thee from the golden round"—that is, she will lend him her own, more ruthless nature, in order that what he deserves will come to him more quickly. From Lady Macbeth's assessment of her husband, we as the audience can truly see how the act of pursuing his ambitions changes him. The Macbeth that Lady Macbeth speaks of "wouldst not play false," and yet Lady Macbeth convinces him that he must "look like the innocent flower / But be the serpent under't," taking advantage of Duncan's presence at their castle to murder him. As Macbeth prevaricates, Lady Macbeth impugns his masculinity—"when you durst do it, then you were a man"—and prevails upon him to "screw your courage to the sticking place" and murder the king.
The murder of Duncan marks a turning point in the play, and for Macbeth. The famous "dagger" soliloquy, in act 2, scene 1, foreshadows the madness which will later overcome Macbeth as a result of having pursued his ambitions with evil deeds. The "dagger of the mind" is born out of Macbeth's mental turmoil, and, having killed Duncan, he hallucinates a voice saying, "Macbeth shall sleep no more." From this point in the play, Macbeth's guilt only increases. Having committed one murder in pursuit of his ambition, he seems to lose grip on reality. Soon, he is ordering the murder of Banquo and Fleance, also obstacles to the prophecy. Lady Macbeth attempts to reassure him—"what's done is done"—but the "scorpions" in Macbeth's mind cannot be calmed. In committing murder in pursuit of his ambition, Macbeth has assured that he will have no joy of what he gains. Where ambition leads to evil, it transforms a person for the worse. Macbeth, a man who never wished to do wrong in pursuit of his goals, is consumed by his own guilt. Even Lady Macbeth, who thought herself so ruthless, eventually descends into madness, as is seen when she asks, "Will these hands ne'er be clean?" While awake, she may be able to reassure Macbeth that he need not worry, but her unconscious mind expresses her true understanding of what they have done.
Ambition in this play, then, is an all-consuming force. It transforms a good man into a guilt-ridden, fretful, violent one, and in allowing ambition to lead him into evil, Macbeth guarantees that he will never be able to enjoy what he has. Lady Macbeth, who urges her husband to pursue his goals, succeeds in destroying both him and herself.