"is that"
Avoid using "is that" phrases in your writing.
Instead of:
One of the most important themes of To Kill a Mockingbird is that one person can't change the world, but one person can have a profound effect on others, which, in turn, can change the world.
Write:
To Kill a Mockingbird shows us that one person can not change the world, but one person can have a profound effect on others, which, in turn, can change the world.
Instead of:
"One reason why Atticus Finch is a great character is that he is a brave and moral character."
Write:
"Atticus Finch is a brave and moral character."
Instead of:
"The problem with Romeo is that he is unstable."
Write:
"Romeo is unstable."