To write a good Instagram ad copy, starting with a clear objective and understanding of the target audience is essential. Begin with a compelling headline or hook that grabs attention and makes the audience want to learn more. Incorporate relevant hashtags and mentions to increase visibility, and consider using a call-to-action to prompt users to take the desired action, such as visiting a website or making a purchase. It's also essential to use high-quality visuals that align with the brand's aesthetic and convey the intended message.