OK here's the stuff I am aware of:
- XHTML/CSS, no tables in layout, CSS code linked from the separate file, no useless junk code, the less errors in validation the better.
- <title>, <meta>, <h1>, <h2>, <p>, and other HTML tags properly used.
- <a href="..." title="..."><img src="..." alt="..." /></a>
- template/theme consistency through the site
- good hierarchy of navigation and subnavigation which should reflect on the good organization of content
- sitemap.xml
- keep the outgoing links per page on the site the least possible.
- content/category hierarchy shouldn't go too deep (cat/subcat1/subcat2/.../subcat666)
- text content should be original/rewritten instead of fed by rss or copy/pasted
- user rememberable and seo friendly url's like food.com/pizza/carbonara.html instead of food.com/index.php?cat=1&item=2
That's it more or less for on-site stuff.
Am I missing something?