Reading points: some matters to consider as you read:
The novelty of the tragic hero's being also the play's greatest villain.
Macbeth's heightened imaginative sensibility: his contact with the supernatural or the visionary throughout the play.
Again, the depiction of civil conflict (as in 1 Henry IV and King Lear): a nation divided against itself.
The prominence of blood or "bloodiness" throughout the play.
Imagery of sickness and disease, and also nature and the unnatural.
Macbeth and Lady Macbeth as deeply committed and "profoundly in love."
Lady Macbeth as "unsexed": consider especially her apparent cruelty and other "unfeminine" behavior. Consider Lady Macbeth's complicity in Macbeth's ultimate undoing.
Undertones of sexual disharmony or sexual dysfunction between Macbeth and Lady Macbeth.
The play's repeated concern with different notions of manliness.
Different ways the play has great relevance for us all: how is Macbeth representative of all humanity? Or at least of a very large proportion of humanity?
The play's depiction of powerful guilt, in both Macbeth and (eventually) Lady Macbeth as well.
Hints of nihilism or existentialism: see especially 5.5.19-28.