Starting a blog is a great way for an author to keep potential readers and current readers up-to-date with what they are doing. What you shouldn’t do is wait to start one until you are ready to release your book. You should start the blog while you are currently writing your book. You need to build a following and an interest in your work.
You don’t need to post something every day; twice a week or even once a week is fine. As for content, post short excerpts from you wip, writing tips and advice you find helpful, books you are currently reading, links to websites for writing help and advice, and writing quotes from other authors. You can also post guest blogs from other writers. Remember, as a writer you are professional, so keep your posts professional.
I find WordPress to be the easiest to use and it is free. You can set it up so any posts you make show up on Twitter and Facebook.