Lets pretend that you're selling a product targeted at fishermen. There are probably 3-5 top forum communities where your customers hang out. You should:

• Have an account in those communities with links back to the landing page you designed for those customers.
• Build your reputation in those communities by answering questions from community members. You can even find ways to work your solution unto the answers you make in those communities without being "spammy".
• If the community has an "Offers" section post your offer there.