Train your staff adequately and establish style guidelines for consistency and clarity (e.g. avoiding library jargon, using consistent acronyms or none at all).
Designate a point person to offer some editorial oversight on public blog posts,
Integrate the blog with the library’s website by providing easy links to the library catalog and other features.
Use “soft opening” techniques to introduce your blog to the public. Launch by putting the blog up, adding a few posts, and adding links from the home page…then really ramp up advertising after a few weeks of regular posting from staff and/or users.