1. Watch your sentence patterns. No two sentences should have the same pattern and cadence within a paragraph. Use simple sentences, complex sentences, compound sentences, complex compound sentences, fragments to keep the words flowing.
A sample from my story Symbiote to be published in the YA anthology Unlocked in August:
Standing on the highest roof in the city, I leaned over the side and peered down. Far below me, clouds swallowed up the lights and noises of the city. My hands clenched, nails digging into my palms, tears streaming down my face. Lost. Alone. Empty. I felt as if the world had devoured me and left me to die.
2. Watch for echo throughout the paragraph, the scene, the story. Cut out or change words to keep things fresh.
I recently read a battle scene that contained the word titanic twice and titanically once. The whole scene sounded riciculous.
3. Watch for similar subjects within your sentences. I read a book where every sentence had the POV as the subject.
Thomas looked around the room. He saw the book on bedstand. He wondered what it could be.
4. Watch for weak verbs. Words like was, were, seemed, looked, had, etc. make for very boring prose.
"Darkness crawled along my skin" is more active than "The room was dark."
5. Watch for too many words.