Darkness indicates something bad is about to happen and light is associated with life and God.
Lady Macbeth, for example, asks "thick night" to come with the "smoke of hell," so her knife won't see the wound it makes in the peacefully sleeping King (act 1, scene 5). The literal darkness corresponds to the evil or "dark" act she plans to commit.
As seen on (act 2, scene 1). As Macbeth wonders if his mind is playing tricks on him, the dagger becomes covered in imaginary blood, which anticipates the way that very real daggers will be soiled when Macbeth murders King Duncan.
Eventually, blood symbolises guilt as told by macbeth after murdering Duncan, that even "Great Neptune's ocean" could not wash away his stain of guilt.
The play is fixated on what happens when family lines are extinguished, which is exactly what Macbeth has in mind when he orders the murders of his enemies' children.