The undersigned has a good article on optimizing your WordPress blog for search engines. It also has a collection of SEO articles from other sites including mine.

Some quick tips I would like to give you are

• select a permalink structure with the post title in it. Do not change your permalink structure once you have selected it as changing it will probably invalidate all of the links coming to you
• make sure that your post title comes before your blog name on your title
• Use keyword rich post titles
• use

  tags for your blog and post titles

• make proper use of alt tags. End them with a period (.)
• Use tags on your blog. I recommend Ultimate Tag Warrior.
• Use Related posts plugin which will help search engines to digg deeper into your blog
• Use Google Sitemap Generator to let Google know whenever you update your blog. Signup for and add the sitemap that the plugin generated for you. Additionally, Elliot Kosmicki offers a script that will convert your Google sitemap into a Yahoo compliant sitemap that you can submit to Yahoo.
• Use Landing Sites to show related posts to visitors search on your blog

Also check out my Search Engine Optimization (SEO) Category for more interesting posts.