There are loads of ways-

Keep a relevant blog.

give your book a definite publication date

Get reviews (you can send review copies securely to reviewers using Net Galley)

I think You Tube is a great way to promote anything, especially books.

Thanks Luke, but I was looking for paid methods. I already released the book, I want traffic fast and I'm willing to pay. I already considered solo ads. Any idea would be appreciated.

Hi chris ,

Surely a loads of ways,

But what about facebook ads ? Solo ads too is great way to go.

Banner ads - find sites relevant to your offer and purchase ad space
Solo ads - find people who are actively building a list or have products similar or complementary to yours and offer to pay them for the mailing
Facebook ads
Bing ads
7Search and other second tier search engines
PPV traffic -> squeeze page -> your offer
Outsource tasks that may relate to long term traffic: SEO, video marketing, content marketing
Pay for pinned posts in FB groups and popular fan pages
Pay for sticky posts in forums
Pay for renting a link in the signature of active members in forums (where available)
Promote your videos on Youtube using their ads platform
Set up cross sell promotions with other successful product owners
Set up a CPA offer and invite affiliates you trust to promote it
Create a content rich website and promote it via Adwords -> subscribers -> your offer
Create a software that your audience absolutely needs and give it away for free (but require an email for registration)
Find successful JV brokers and make a deal with them
Write newsworthy press releases that relate to your niche audience and use a good service for distribution (like PRWeb)
Buy websites with traffic

-Gabriel