Is larger than your own, but not ridiculously huge. Aim for a blog that’s roughly five to ten times the size of your own. If you have 100 email subscribers, aim for a blog with ~1,000. If you’re aiming for blogs (like Forbes) that are more like a thousand or more times the size of your own, that’s a bit too ambitious when you’re brand new to guest blogging.

Is on-topic for you. While you might gain some benefits from writing for a blog about cats when your blog is all about gadgets, there’s not going to be a lot of audience crossover, so you shouldn’t expect to see much of a gain from that time investment.