To achieve a high-quality, accurate advertisement, the most effective solution is to give a list of features that should be highlighted. In prompt engineering, this is known as providing 'input data' or 'grounding.' Without a specific list of features, the AI will likely 'hallucinate' capabilities for the sports watch---such as a 100-day battery life or a built-in laser---that the product does not actually possess.

By providing a concrete list (e.g., 'GPS tracking, heart rate monitor, 50m water resistance, and sapphire glass'), the user provides the AI with the raw materials needed to construct the ad. This shifts the AI's role from 'fictional writer' to 'creative editor.' The model can then focus on persuasive language and structural formatting rather than inventing technical specifications. This is the standard professional approach for marketing teams: use the prompt to establish the 'facts' and let the AI handle the 'flair.' It ensures the resulting text is both creative and factually grounded, which is the primary requirement for any commercial advertisement.