First, finish your manuscript - have a few friends or members of your writers group critique it. Edit, polish and edit again.
Meanwhile, research the publishing industry. Know your market.
Build up a strong web-presence, to establish your audience and and potential buyers.
Find an agent suitable for your kind of work, who'll help place your MS with a publisher.
If all else fails, marry a footballer. Your book is then bound to sell, even if it's 100% rubbish. :)