Think of a paragraph as a mini-story within your larger story. It should have one main idea, and every sentence should support that idea. If you find yourself drifting to a new topic, start a new paragraph.
When I write, I always ask myself: "What's the point of this paragraph?" If I can't answer that clearly, I know I need to tighten things up.
The Topic Sentence
Every good paragraph starts with a topic sentence. This sentence tells your reader what the paragraph is about. It should be clear and specific, not vague and general.
Instead of saying "Exercise is good," try "Morning exercise boosts your energy for the entire day." See the difference? One gives you actual information.
Supporting Sentences
After your topic sentence, you need supporting sentences. These provide evidence, examples, or explanation. This is where you show your reader WHY your main point matters.
Use specific details. Instead of "People like coffee," say "Millions of Americans start their day with a cup of coffee." Numbers and specifics make your writing believable.