How do literary and dramatic conventions inform the development and characters in Macbeth?

Two of the most significant literary and dramatic conventions that Shakespeare uses help to establish and inform characterization in Macbeth are asides and soliloquys which help his audience to chart characters' development throughout the play.  Immediately after he speaks with the Weird Sisters, Macbeth begins to speak to himself in a series of asides where we learn that he is, at least, able to contemplate any violence that might be necessary to make him king; however, they also allow us to witness his hope that "chance may / crown [him] / Without [his] stir" (1.3.157-159).  In other words, he believes that fate might bring him the throne without his having to do anything to get it; he is, initially at least, not prone to violence.  Once Duncan names his son as his heir, though, Macbeth's next aside reveals his intention to act on his "black and deep desires" (1.4.58). 

Lady Macbeth's soliloquy after she receives Macbeth's letter, as well as the news that he and Duncan are on their way to her home, shows us just how easily and quickly she commits to violence when she describes the "fatal entrance of Duncan / Under [her] battlements" (1.5.46-47).  Further, her request that any murderous spirits come and "unsex" her, helping her to behave in a masculine way, without remorse or compassion, emphasizes her ruthlessness, a full sense of which we would not have were it not for these lines. 

Later, after the murders of Duncan and Banquo, we can see the development of Macbeth's commitment to violence and brutality when, in an aside, he determines to punish Macduff by attacking his home and giving "to th' edge o' th' sword / His wife, his babes, and all unfortunate souls / That trace him in his line" (4.1.172-174).  He will no longer wait to consider once he resolves on violence because this is how Macduff escaped him.  At this point, too, he is not even being honest with his wife, and so we require his asides and soliloquys to help us know what he is really thinking and feeling.

Further, Lady Macbeth's aside after she and Macbeth have become queen and king shows that she is not as happy as she thought she'd be.  She says, "Naught's had, all's spent, / Where our desire is got without content" (3.2.6-7).  They got what they wanted, but they cannot feel content because there are still threats (via Banquo and Fleance) to their power.  Lady Macbeth actually now feels that it would be better to be dead than to destroy others and only achieve "doubtful joy." 

Finally, it is Macbeth's final soliloquy, after he learns that his wife is dead, that shows us his true feelings.  His violence and striving has not satisfied his greed, has not brought him happiness.  In fact, he has now determined that life is, essentially, meaningless.  He calls life "a tale / Told by an idiot, full of sound and fury, / Signifying nothing" (5.5.29-31).  In other words, he feels that life is like a purposeless story that makes lots of noise and seems very dramatic but really lacks any point.

Shakespeare's use of these asides and soliloquys (and others not discussed here) is one of the biggest devices he uses to establish and develop character.