In Shakespeare's Macbeth, the use of the supernatural is effectively used to create interest
and suspense. The theme of the supernatural is developed through character and plot- the
witches and the apparitions. Both of these influence Macbeth; at first the supernatural
motivates Macbeth to seek power and then the supernatural takes part in his demise.
You've begun to set down the premis for an interesting essay. Now bring some focus to your ideas:
In your second sentence things begin to go awry:
The theme of the supernatural is developed through character and plot- the witches and the apparitions.The parallelism that you have drawn here between character/plot and witches/apparitions begs for further development. Do you mean by this that witches are characters and apparitions are plots? If so, then a reader expects some explanation here. Otherwise, your following sentence leaves the reader wondering exactly how your parallelism works: "Both of these influence Macbeth;" How?
Also something to ponder here, can you really write about "apparitions" as plots? They definitely serve to further the plot, but are they the plot itself? Again, explain ... And what about other plot influences? (e.g., Macduff is "not of a woman born," etc.)
If you clearly develop your ideas, you'll have an intriguing beginning ...