In revising your writing, whether fiction or nonfiction, it is crucial to hear it. Read it aloud, but also, let it be read to you. There are good inexpensive (I use Natural Reader) and even free programs that will let your computer read a text document to you.
In addition to catching some startlingly obvious errors, you’ll hear repetitions that you didn’t see, you’ll notice if the meter of two different characters’ speech is too similar, and more.
The time spent listening to your work being read out loud—yes, the entire novel—is worthwhile, so don’t skip this step.