Couple things worth adding…

Structure: Use Header tags (h1, h2, etc…) and use them in the right order. H1 is used for the primary header on the page and should only be used once as the title of the page. H2 is used for sub-categories, followed by h3 and so on… Other tags can be used repeatedly, but use them in order of relevance.

Clean Code: Order your sections properly. Header, Navigation, Content, Footer. Then style accordingly with CSS. Unless you want a screen reader to read what in your sidebar first, then you need to have the primary content for the page BEFORE the sidebar content. It doesn’t matter if visually you want the sidebar on the left. It should still come after the primary content, then styled (floated) with CSS to where you want it.

Accessibility marks and “jump to” links: Provide hidden markers and links for screen readers. Label your navigation, label your content area, label your sidebar and assign them ids. These don’t have to be visible in the visual layout but makes it worlds easier for the screen readers to visualize where they are on the page.

Re the “jump to” link: at the top of the page provide a few links (again only visible when stylesheet is turned off) that will allow a user to “jump” to navigation, content area, sidebar, etc… on the page.

Hope those help (or at least make sense)

Lastly, here’s another good blog post re: SEO for designers that I think would make for a good extended read of this one:
http://justcreativedesign.com/2008/06/09/10-seo-rules-for-designers/

(that got long. Sorry. This list could almost go on forever.)