When you do something prosaically, you do it in an ordinary, straightforward way. Some could even call it boring. While your poet friend announces that the sky is weeping, you might more prosaically say it’s just raining.
When you state something without any added imaginative details or flowery language, you speak prosaically. The adverb implies a lack of originality as well. Your poet friend might add descriptive details to all weather reports, but to say it prosaically is to just state the facts. The Latin word prosa, or "prose," is the origin of prosaically and its related adjective, prosaic.