Writing a blog post based on your own research paper is actually a good way to promote the study. This is common practice, and many authors do this for research promotion. Ideally, this should not be considered self-plagiarism as long as you are using content from a published paper and are crediting the source. The general practice in such cases is to add a sentence at the beginning or end of the blog post stating that the post is based on an article published in so-and-so journal by the same author, with a link back to the journal article. However, if the copyright of the paper rests with the journal, you should read the journal guidelines for reuse of the article. If the guidelines state that you need the editor's permission, it is better to do so, else you might end up making a copyright breach.
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