Paragraphs are the building blocks of written works and are defined as a group of sentences that support a single controlling idea. Effective paragraphs include a topic sentence to introduce the main idea, sentences that develop and elaborate on that idea through examples and analysis, and a concluding sentence that wraps up the key points. Coherence and flow between paragraphs can be achieved through the use of transition words, parallel structures, consistency in style and tone, and repetition of key ideas.