There is no place that describes "Survival of the Fittest" better than the web. Much like any competitive environment, those that execute on the web survive while those that don't, well, don't. If you're serious about developing a presence for your site, you are going to have to adapt to what the fittest entities on the web are doing to both survive and thrive.
While it may sound a little (or a lot) Darwinian, the websites that adapt and execute the best are the ones that succeed. While site design plays a big role in the game, the defining issue always comes down to the execution of web marketing strategies. These strategies are always multi-faceted depending on the type of business but still fall generally along the same lines.
The crux of successful web marketing lies in two areas; developing quality content both on and off the site and building inbound links to the site. The quality of published content, while it can play a role in the search engines' algorithms, is pointed more toward developing credibility and trust with readers.
In terms of what the search engines look for, inbound links play one of the most significant roles. These links rely on quality content to survive and are considered as "votes of approval" from the originating site, which links out because it deems the receiving site as both worthy and relevant. Because these links are considered by the search engines as objective third party referrals, their weight plays a significant role in how pages fare on search engine results pages.
By combining these two characteristics, quality content and inbound links, your website can win the battle of the "survival of the fittest".