Perception and reality is one of the more seminal themes of Macbeth. The first example of perception and reality is the entire episode with the witches' prophecies. What the witches say and what Macbeth and Banquo construe them to mean are two entirely different things. Macbeth especially "mis-perceives" reality. The Polanski film version of the play and the witches' prophecies treats reality and perception well--especially with the scene of the refracting mirrors.
Another instance occurs as Macbeth follows the dagger to King Duncan's chambers. In reality there is no dagger, but Macbeth perceives that there is. We know it will turn into a "dagger of the mind."
Another instance is Lady Macbeth's blood stained hands. She wrings and wrings her hand but cannot get the blood off. Yes she is sleepwalking, but it is indicative of her conscience trying to process the bloody deed.
One final example is Banquo's ghost at the Macbeth banquet. In reality there is no ghost, but Macbeth's sick and stained conscience makes him perceive that there is one.
There are a number of different ways you might handle a discussion of reality and perception, I've started you off considering the plot based ones.