The initial purpose of the blog is to drive more participants to LL SE. I say "initial" because it should be OK to change the blog's purpose once we have sufficient website traffic. (That will take a while, though.)
More users should mean more questions and answers (hopefully of high quality). For this reason, an important type of content on the blog should be based on high-quality answers that were submitted to the site.
The blog can also be used to highlight high-quality questions that have not received an answer yet, and describe ideas for language-related questions, such as the creation of website with minimal pairs in arbitrary languageswebsite with minimal pairs in arbitrary languages.
Updated: Possible more detailed guidance on how to contribute, like this page on Sci-Fi's blog.