What everyone said:
You need a website (fairly expensive)
or a blog (free).
Readers will come to the site if they have seen your name or your book title and they are curious.
Help these good people out, for Pete's sake.
When they arrive at your site let them find your book covers sitting there right on the front page.
Link to sellers. Link to a summary of the book and to an excerpt.
You also need a link to your e-mail,
(your separate author e-mail account,)
because reviewers and book groups and indie bookstore owners and so on want to talk to you.
You should get a cheap stat counter to track where your hits are coming from.
You should reserve your domain name.
Now.
There are two general ways to lure folks to your site.
I. Get reviewed.
If you ask what publishers do to promote books, the bare minimum is, 'they send out ARCs.' This is the biggest return on investment. It works.
Find out where your publisher is sending your ARCs for review.
(1) Check each of these sites to make sure they are still in business. Clear out the deadwood. If you've got half a dozen books under your belt and your ARCs have been going out to minor sites who never review them, weed those sites out as well.
(2) If someone has reviewed you intelligently, get their snail mail address and put them on the ARC list.
(3) Make sure the most widely read and respected review sites are on the list. Find less-well-known folks who review exactly what you write -- Google books like your own and see who reviews them -- and get those added.
If your publisher is not sending out ARCs, you should be doing this.
II. Provide content
If you write about fairies with cross-bows, you have done a lot of research on crossbows. Put the research on your blog. Folks interested in crossbows may buy your book, of course. Just as important, they will link to your site on their blogs. This linkage bumps your site upward in web searches.
And talk about books you love. Books that are similar to your own. You don't have to do 'reviews', but if you discuss the field in which you write, you can mention the best books and link to those authors' websites.
People who are interested in vampire fairies or fairies who knit or fairies in the context of law will be drawn to the site by the keywords of your text and by the names of other authors.
If you become a reliable source of history or legend or technological detail or just a comic pick-me-up, you will add value to the world. At worst, you have acted generously. At best, readers are going to come for the discussion, notice you're a writer, and buy the book.