I recently had to do this when I was writing about a product.
What I did was find articles about the product, visit the products main website, search for videos that covered the product, and looked up reviews. After I did all that, I chose what I liked and disliked about the product and wrote about that.
Though it depends on your niche, I am sure that you can take a similar approach to most topics. At the end of the day though, if you are not an expert on a topic, you better be a great writer. Otherwise there would be no reason for anyone to read your content over somebody else's.