Since you are a web designer, I hope the mods will not consider my post as self-promotion if I place here a link to one of our services describing
Human & Search Engine Friendly Web Design Services and a tutorial
The strong link between Usability & SEO.
Also you can find excellent tips at our site review request in our own forums:
SEO Workers would appreciate review.
I am sure you will find there the best tips around concerning human and search engine web design.
Just my two cents.