Short Answer 
To write an effective paragraph, start with a clear topic sentence that introduces the main idea, followed by concrete evidence that supports this idea. Use transitional phrases to ensure coherence between sentences and conclude by reiterating the main point to reinforce the paragraph’s message.
Step 1: Introduce Your Main Idea
Begin your paragraph with an introductory statement or thesis, known as a topic sentence. This sentence should clearly communicate the main idea you wish to convey and serve as a guiding pathway for the reader. For instance, you could start with a statement like ‘In the field of astronomy, much has been discovered about the planets,’ as it sets the context for the rest of the paragraph.
Step 2: Support with Evidence
Follow your topic sentence with sentences that provide concrete evidence to support your main idea. This can include qualitative and quantitative data, examples, or facts that relate directly to your opening statement. Ensure that each piece of evidence is relevant and elaborates on the theme introduced, thus enriching the reader’s understanding of the topic discussed.
Step 3: Ensure Coherence and Conclude
To maintain coherence throughout your paragraph, use transitional phrases to connect your ideas smoothly, such as ‘moreover’, ‘however’, and ‘on the contrary’. Finally, wrap up the paragraph by tying everything back to your main point. You might restate the primary argument or emphasize the significance of the evidence presented, ensuring that your conclusion resonates with the reader.