Transitional words help improve writing coherence by smoothly connecting ideas between sentences and paragraphs. Some transitional words continue an idea, indicate a change in thought, or conclude. Words like "furthermore," "moreover," and "in addition" continue reasoning, while words like "however" and "but" contrast ideas. Words like "in conclusion" and "therefore" signal the end of a discussion. Using transitional words and phrases helps writing flow logically from one point to the next.