How do you find out who your audience is? How do you target a specific audience. Lets say I want to SEO a site for people in their 30ies - 40ies to sell them a particular product.
You can check your stats and begin analyzing from there. See what keywords people use to find your site, how much they stay when they visit it, do they buy something, etc.
You usually can find about anything you need with nicely made Pools placed on your site. Just leave them on the site for some time and you will be able to find your answer. If you want to seo for a particular audience you will have to understand that audience particular needs, questions etc, develop the content based on the gathered info and implement them in your link building effort also.