You can start figuring out your target audience by focusing on reading the reviews in your niche. You can also spend some time on forums and read the comment section on blogs that cover your niche topics. If you notice some unanswered questions emerging over and over again, write them down. Your audience needs them answered, and you can do it for them. Or you can do an online search for the best niche blogs and see how they are structured.
For example, let’s say you are big fan of the South Beach diet. That may have been a great niche to get into ten years ago, but now that diet is considered passé. People have moved on to other diets.

For instance, if you choose to promote your content via paid ads, then that’s a cost you have to account for. You will have to compare how much you’ve spent to promote each piece of content or to generate each purchase against how much commission you’re getting for each referred sale.
Not only that, but it also helps with your content creation if you are already familiar with the products and services. If you are a genuine fan of whatever you are trying to convince others to buy, it will go a long way, and users will be able to sense your enthusiasm before they too get behind a product.