There are several examples of both good uses of power, and the abuse of power. First, Macbeth himself shows us both the good and the evil. In Act I, he uses his power to lead his army to victory for King Duncan. Because of his bravery in battle, he is rewarded with the title Thane of Cawdor. As the play progresses, Macbeth uses his power to rid himself of potential threats to the throne (Duncan, Banquo, Macduff's family). We find out in Macduff's speech to Malcolm that he has a reign of tyranny, and people fear him. This abuse of power leads to his death.
Duncan, Malcolm, Banquo, and Macduff all serve as good examples of using power. Duncan seems to be a fair and just king, punishing the treacherous and rewarding the loyal. Macolm reveals his desire to restore order to Scotland, using his power to organize a march against Macbeth. Banquo hears the prophecy that his sons will be kings, and chooses to do nothing about it. He lets the natural course of life decide who will be king when, rather than taking that power into his own hands. Macduff shows himself loyal to his country and family above all else, and is rewarded by killing Macbeth.
Negative examples also include Lady Macbeth and the Witches (or Weird Sisters, depending on version). Lady Macbeth coerces her husband to defy the natural order of the universe and kill the king, seizing power that was not meant to be theirs. The witches use their power to meddle in the affairs of Macbeth and Banquo, purposely setting Macbeth down a destructive path. These examples show the consequences of abusing one's power -- despair to themselves and others.