Well, start with a strong concept. If you want to write a hurt imprint fanfiction, think about what could go wrong with an imprint. Is it a case of unrequited love within the imprint? Or perhaps the imprint is a curse instead of a blessing? Develop your characters around this concept. Let them have flaws and desires that are affected by the hurt of the imprint. Also, use vivid language to describe the pain. Instead of just saying 'it hurt', say 'The imprint felt like a thousand needles stabbing his soul every time he thought of her'.
To write a good hurt imprint fanfiction, you need to understand the nature of imprinting first. It could be a spiritual, emotional or even a physical connection in your story's universe. Then, introduce elements that can cause harm to this connection. This could be betrayal, misunderstanding or a malevolent force. Build up the tension gradually. For instance, start with small signs of discomfort in the imprint and then escalate it to full - blown pain. Use dialogue to show the characters' struggle with the hurt. For example, 'I can't bear this imprint anymore. It's killing me inside' shows the depth of the pain they are experiencing.
First, focus on the emotional aspect. Really dig deep into how the characters feel when the imprint is causing them pain. For example, describe their inner turmoil, like 'His heart ached as the imprint seemed to burn with every wrong move she made'. Second, create a conflict that is directly related to the imprint. Maybe it was forced or there are external factors trying to break it. Third, don't be afraid to make the characters grow from the hurt. Show how they learn to either accept or change the situation of their imprint.