What is key to focus on in the development of the relationship of these two characters is the way that at the beginning of the play it is Lady Macbeth who is the main driving force behind the crime of regicide and Macbeth's ambition. As Act I makes perfectly clear, although Macbeth himself receives the prophecy of his future greatness, it is only thanks to the encouragement and berating of Lady Macbeth that he actually goes through with the plan and kills Duncan. In fact, in Act I scene 7, after a lengthy soliloquy, Macbeth actually resolves to not carry out the murder out of fear of the possible consequences. Lady Macbeth responds to this caution in many different ways, using open verbal attack, mocking his character and then moving on to encouraging him about the surety of their success:
But screw your courage to the sticking-place
And we'll not fail.
In Act II scene 2, when Macbeth enters having killed Duncan, Lady Macbeth insults him for being unable to smear the grooms with blood, saying to him "Infirm of purpose!" Thus, at the beginning of the play at least, it is clear that Lady Macbeth is the more dominant member of the marriage and it is she that coaxes and urges her husband on to pursuing the prophecy he is given.
However, later on, it is clear that the positions reverse in this marriage. With the murder of Banquo, which Macbeth organises by himself without reference to his wife, things begin to shift, and Lady Macbeth retreats into the background of the play whilst Macbeth shows he is left to pursue his evil crimes and atrocities alone as he gradually works up from organising the death of Banquo in secret to committing open atrocities, such as the murder of Macduff's family. Lady Macbeth is left as a figure haunted by her crimes who dies as a result.