DO read a few posts from the blog before you send something. You run the best chance of having your post published if it resembles what they typically run. Things to pay particular attention to include word count, reading level (beginner vs. advanced), and voice (serious, kooky, snarky, etc.). If the blog publishes guest posting guidelines, read them (duh).
DO establish a relationship before you write. This isnโt strictly necessary, but if youโre trying to get a guest post published on a more exclusive blog, youโll have better luck if the editors already have some familiarity with you. You could start by commenting on the blog, linking to the blog from your own, or engaging with the editors/writers on Twitter.