Join Online Communities and Forums

This only requires your time and nothing else. You can share your knowledge and expertise with many online communities as well as your website. You can get free advertising when you go to forums that have the same subject or niche with your site.

Share your two cents and let them see how knowledgeable you are with the subject. As you build your reputation, you also build the reputation of your site, making it a reputable and honest business that could be frequented and trusted by many people.