No buts--the publisher isn't going to do it, it's up to you.
So, you've begun a blog, right? Joined some social networking?
Of course if you've begun a blog you have to add to it regularly so you can gain followers, not lose the ones you have, and of course provide some sound, helpful, interesting and hopefully at times amusing content.
But, every writer has his or her day when it just won't work. Maybe you have the dreaded blog block.
What to do?
I focus mainly on fiction so I'll give you some ideas in that area - not that I've already done all these, but there are some I've done and some I'm planning on doing. So here you go:
One simple thing for a fiction writer is to do is to quote an entire short scene from one of your novels as a teaser. This would encourage your readers to buy your book and using an excerpt could be a great way to illustrate some point you're making. Just make sure the excerpt you choose relates clearly to the point you're trying to make.
Here's another thing. If you're writing genre, think creatively about what you might write about that links to it.
Science Fiction writers can link to the world of science and emerging discoveries. Or they can write about strange anomolies or government cover-ups of UFO's and what about those crop circles?
Mystery writers might create blogs on crime stories they see in the paper each day or a death that is a medical mystery and could be something else... Or they could consider writing about the newest forensic science.
If you choose romance you can put posts on your blogs about foods which are thought to be aphrodisiacs or cooking for your lover or both. If you're adventurous you might blog about the karma sutra or about romantic get-aways; trips for lovers to share.
Might take a bit more imagination, but all you need to do really is to ask yourself as you write your novel, what are the angles? Are there particular foods or locals associated with your novel? Is there a certain culture you use in your story you can extrapolate on in your blog? Travel? A certain profession? An event such as the olympics, an electronics expo? A swim meet?
So you see, you can cover subjects far beyond what the book you write is actually about. Anything linked is fair game.
Oh, and you might consider reviewing books in a genre similar to the one you're writing in. The name of a famous writer writing in your field will attract readers from the search engines to the review. Reviewing the books of the famous to the lesser known can attract readers.
Don't forget to ask authors of other blogs to participate in cross-promotion. You write for their blog, they write for yours. Very helpful.
Sprinkle in helpful links as well. I know, I know, my blog hasn't had a whole lot of that, but I post a lot of links at Twitter - like contest links, website links, language help links. I enjoy helping people find the things that are useful to them.
If you have access to them, offer freebies to folks who read your blog. You might even think about having a contest in which you offer a 'gift basket' of items that relate to your book. Could be free Ebooks, sample chapters, poems, anything helpful.
So, sit down with yourself, think about it, and come up with your own creative ways to promote your work online and off. It really is up to you.