Really though:
1. Look at the copy of your competition within that niche. Ask yourself, what type of language do they use? How do they incite interest, inspire action, and how are their ads and copy structured.
2. Look at the questions and problems you see spoken about in your niche's communities. At its root, all problems and solutions are based on how people FEEL, and all decisions are made emotionally as well. What triggers are there that you can tug on? What provides them relief and how can your potential solution add to that?
3. Are they educated? Are they "dumb"? Most buyers online are suspicious, so you need to use the stuff you learned above, to show you understand their problem, and you are their goddamn savior, leader, and personal confidant. When shit goes down, you are the one they can trust to hide the body.
4. Sit down, have a clear idea of what you want to convey. Break it down into a few sections. Then just WRITE. This is where the whiskey comes in if you need to be loosened up a bit. Ask them questions, give them answers, put your heart into it. Copywriting needs to FEEL like you are reaching through the screen and slapping them with the truth.
5. Depending on whether you're selling a high tag item or just looking for a free lead, you have to gauge how much persuasion will need to go into it. Use your competition as a foundation and test your creativity by looking for alternative ways to do what they've done.