In Macbeth, what technique does Lady Macbeth use to boost up Macbeth's hunger for his ambition to become the next king?
Lady Macbeth tells Macbeth that she will support him and help plan Duncan's murder in order to secure the throne for Macbeth. When Macbeth becomes fearful or guilty, Lady Macbeth calls him a coward in an effort to embarrass him into action. This could also be an example of reverse psychology. Calling him a coward may induce him to behave bravely. She wants him to feel ambition above all other emotions. This is how she deals with Macbeth.
What is more significant is how she deals with herself. In order to be this voice of dissent in Macbeth's ear, Lady Macbeth conditions herself to behave without conscience and even goes so far as to wish to become supernatural or less like a woman in order to carry out this scheme.
Come, you spirits
That tend on mortal thoughts, unsex me here,
And fill me from the crown to the toe top-full
Of direst cruelty! make thick my blood;
Stop up the access and passage to remorse, (I.v. 390-394).
Lady Macbeth uses psychological manipulation to influence Macbeth. There will always be a debate on how much of a role she plays in the murders Macbeth committed because he does the deeds. There is also an ongoing debate on how much responsibility the witches have.
You should also focus on how Lady Macbeth manipulates herself in order to become immoral enough to go through with it all. So, her technique is two-fold. She manipulates her husband but first must manipulate herself. Asking spirits to "unsex" her is a call to make her more masculine (more physical like a soldier) and less human. An evil spirit does not have to wrestle with a conscience. A human does.