Google are trying to kick the crap out of search. They don't want 'cheap affiliates' or Information websites that harbour crap..
So basically:
Create good content>>Keep your visitor on your site for as long as possible>>Provide links to pages on your website that compliment the page your creating.
The longer you can hold a visitor entertained the higher you'll rank! - there are many other factors, but this is one of Googles newest...