4. Sites should have a clear POINT!
Driving users to your site only to have them miss your point is an Internet felony.
Your core competancy or core offerings should be immediately obvious to anyone jumping into your site from any page they land on.
Site owners should have a direct call to action on every relevant page that easily walks their audience from identifying your point, to understanding your point and finally agreeing with your point.
It sounds so obvious but as sites start to skew their content for SEO popularity they are introducing textual noise that is obscuring the point.
Here's a humerous example of someone that has blended both ideas perfectly.http://isitfriday.biz/
The purpose of that site is reasonably straight forward, and to demonstrate it's organic searchability, try googling "is it friday".
You must have a clear reason for taking up your users' time and it should be obvious to them within 3 seconds.
You can perform a quick test on yourself to see if you are creating content that helps deliver your point. Ask yourself one question:
Is the content I'm writing something I would naturally say to my client in person or am I selecting words and phrases that are designed to impress Google?
The ratio between those two answers is approximately the same as the inverse ratio to your website's efficiency at demonstrating your point.
Remember that Google can't be converted to an active consumer of your message, and human's won't digest your content like Google will.
It sounds obvious but your site should be tailored for the humans you expect to impress and not the engines that will get them there.