I get contacted about WordPress SEO a lot – and please email me if you would like some help with SEO on your WordPress site.
Anyway as a quick guide, you need to get the Permalink settings correct. The default setting is not SEO friendly: http://example.com/?p=N
In the Settings / Permalinks panel you can choose a Permalink setting. I have mine set to: /%year%/%monthnum%/%postname%/ so you see above the URL is: http://sarawright.com.au/2011/05/wordpress-seo/
I also use the Google XML Sitemaps plugin, which generates an XML sitemap, and which I then submit to the main search engines (which the plugin explains).
I have been trying out a couple of different WordPress SEO plugins: SEO Ultimate and All in One SEO Pack. I originally went with All in One SEO as it has been downloaded so many times, and has 4 star rating by over a 1000 people. Its works well, is easy to use BUT I much prefer SEO Ultimate. It does so much more: SEO Ultimate gives you control over title tags, noindex, meta tags, slugs, canonical, autolinks, 404 errors, rich snippets, and more.
I particularly like the 401 module – great for keeping an eye on any page not found errors. And you can set the meta description and page titles for all the pages and posts in one place rather than going into each and every page. It could be a bit complicated and confusing to a non-techy.