Google updates its way of searching the web so often that it is almost impossible to keep up with it.
One key point we picked up recently is that the search engine needs to see at that at least 60% of the content on your website is unique - you write it yourself and it isn't repeated anywhere else on the web. This is harder to do than you might imagine for businesses that sell products with standard descriptions for example. A word from the wise (wiser?!) - don't be tempted to repost blog content or even page content to your own site without writing about it in your own words and checking you haven't fallen under the 60% boundary.
Sites that are known as 'content farms' - those that collect text and images from all over the web and feature them, uch as news portals, are bad news as far as Google is concerned. If a content farm is pulling your information, Google will penalise you for it.