One way is to write a really great book, so everyone talks about it and you don't have to do a minute of self-promo for the rest of your life.
Meanwhile, back in the real world...
Spamming will only get you a bad name. Hitting your facebook friends and twitter followers with the same BMB posts over and over again will drive them away. Littering forums with Kindle links and snips from reviews posted by your best buddies is bad, very bad. Advertising fiction doesn't really work. CC'ing press releases to everyone you've ever received an email from is not good. So what does work?
Having more than one offering - that's good. Genuine reviews on amazon & smashwords are useful, but they won't help people to find your work in the first place. Blog reviews are great, as mentioned in previous posts. An effective website is good too - a cover shot, a synopsis, your bio, a press page with a downloadable press release, a sample ... all of these things help. A blog can be good, but it if you write about publishing and being an author, most of your readers will be writers (hi writers!) many of whom aren't interested in your genre or your novels. Fact of life.
A giveaway, posted to your website and linked from facebook and twitter - that can be effective. Free ebook copies on request. Desktop wallpaper featuring a design linked to your novel's cover art (clear this with the artist first, and provide several sizes.)
These are just some ideas. I've been posting articles on writing and publishing to my site for the past seven or eight years, and my website is the top result in many, many google searches. When I put up the page for Hal Junior, my new science fiction novel for kids, it went straight to number one for various searches (mostly Google Australia, but I'll take that ...)
When an aussie parent, teacher or librarian goes to Google and types in junior science fiction, then clicks 'pages from Australia', my yet-to-be-released novel is the very first hit. What's that worth in publicity terms? Even on google.co.uk it's top of page 2, and it's the first actual book after several links to publisher and review sites.
It's taken years for me to generate the traffic and inbound links to achieve this, and who knows whether it's going to be useful long-term? I'm just pointing out that if your website provides things people are interested in, rather than being just a sales page for your novel, they will share the link and send others to have a look.
And on that note, have you seen the weekly science fiction comedy web comic featuring Hal Spacejock? It's only been out four days and it's already #10 in the google search results ...
Simon Haynes is the author of the Hal Spacejock and Hal Junior series (Amazon / Smashwords / other formats)