If a site is professionally built for PEOPLE! Then you will have followed what search engines want by and large.
I and others have been saying this till we are blue in the face.
a) people want well titled pages,
b) people want links that help them identify what will be the content of the page at the other end of a click.
c) People want to know where they are on a site easily
d) People want to be able to navigate around a site easily
e) people want nice small pages that can be read easily and are covering one or very few topic.
f) People want that if a page is large it is split into sub topics and headed so they can skim to the relevant material on page
g) people want links from that page to related pages, if in the middle of the text contextually then better still
h) People would like to see links to other sites that are related to that topic
i) people with usability issues such as impaired eyesight would like to know that the image is a fluffy black and white kitten playing with a ball of yellow string (I bet you can now see that in your minds eye).
j) people want pages that load quickly and run smoothly (good code, but not necessarily WC3 compliant)
(There are other things as well but these are first draft off the top of my head.)
Search engines on the other hand want....... pretty much the same as people
Build for people, and there is hardly anything left to do for the search engines. Search engine friendly site design is basically people friendly site design with some backlinking.