How does Lady Macbeth dominate her husband throughout the play?

Almost the first thing Lady Macbeth does after Macbeth returns home in Act 1, Scene 5, is give him instructions, showing that she is certainly the more dominant partner in their relationship.  She says that, when Duncan arrives, he should "Look like th' innocent flower, / But be the serpent under 't" (1.5.67-68).  In other words, she directs him to appear loyal and good as he always has, but to harbor his murderous intentions in secret.  In fact, the final line of the scene is hers: she tells Macbeth, "Leave all the rest to me."  She will do all the planning of Duncan's murder, and she actually intends to commit the murder herself, believing that Macbeth is too "full of the milk of human kindness" to do it himself. 

Later, when Macbeth decides not to go through with Duncan's murder, Lady Macbeth essentially tells him that he is behaving like a coward and implies that he is not a man.  She says that she would kill her own baby if she'd promised him she'd do it rather than break the promise to him.  In this way, she goads Macbeth into recommitting to the plan.

Even after the murder -- which Lady Macbeth was not actually able to commit, and so Macbeth had to do it -- he regrets his actions and immediately feels tremendously guilty.  Macbeth panics because he could not speak the word "Amen," and Lady Macbeth tells him, "These deeds must not be thought / After these ways.  So, it will make us mad" (2.2.32-33).  She commands him to move on and stop dwelling on what they did because it is in the past.  If they continue to dwell on it, it will drive them crazy.  She coerced him to submit to their plan and then to actually commit the murder himself when he was the one who really didn't want to do it.  Lady Macbeth knows exactly how to dominate her husband, how to stir his pride and ambition and, thus, manipulate him into behaving just how she wants him to.  At least, this is true for the first part of the play.