http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35291the easiest thing from a programmer's perspective are clean and accurate page titles and URLs.
like "mywebsite.com/page-title" not "mywebsite.com/page.php?id=3249
and structure the pages in a common folder hierarchy. like "about-us/our-history"
then make sure the valuable content on the page is all in plain text and formatted well. Instead of just using a larger, bold font, heading text should be in styled <h1> tags and subheadings in corrisponding <h2> etcs...
for meta tags, the description is wicked important. Google basically ignores keyword lists though.
when cross-referencing links on your site, make sure you use descriptive link text.
instead of "learn about dogs,
click here" us "learn about
dogs."
just doing those basics will sky-rocket a site in the rankings. For more detailed quirks, read up on the document linked to in that google aritcle i included at the top of this post.