Search for blogs that cover similar topics. Use a search engine and the search bar on blog hosting sites to find blogs that cover your topic or related topic. Read a few blog posts from the most popular ones, that show up high on the search ranking, have the most comments, or display a readership of 20,000 or more. Get an idea for how much interest and competition there is.
PS: my answer to this question is always… “the better question is… how can my blog help me build a profitable business?” Most of the profits from blogging are not made on your blog, but that’s okay. I don’t believe blogging about making money per se, but about branding yourself and positioning yourself within your niche market as an authority and leader. Once that is established, there are so many ways to move people into your money making enterprises. Email marketing, as you pointed out, is one of the best ways to do this. Sending people to your membership sites, services, info products and coaching programs are all great things to route people into as well.
Hi Sam! I love your site. We should definitely connect. I’m a school counselor and recently launched a site for parents to address pertinent teen topics. Like you, I struggle with the ultimate service I’d eventually offer on my site, but Ramsay’s idea is a great start. He’s absolutely right that people are looking for fresh content for their sites! Best of luck to you and I hope we can collaborate.