“Guest posting” means writing and publishing an article on someone else's website or blog. I offer this on my own site (occasionally) and do it quite a bit on other blogs with audiences that I want to speak to. It's a great way to connect with new readers and get your name out.
Guest Posting is still the most powerful strategy for SEO Ranking, iff you execute it in the right way. And, it should be at the forefront of your mind. I personally recommend you not to limit yourself in your niche/market. Write better content that helps you to position as an authority.