On my previous article for optimizing WordPress for seo i showed how some basic change on wordpress and installing some plugin can improve your website seo.

Now i recommend to use WordPress SEO by Yoast along with those steps.
This plugin have the following features :

• Page Analysis
• Technical WordPress Search Engine Optimization
• XML Sitemaps
• RSS Optimization
• Breadcrumbs
• Social Integration
• Import functionality for other WordPress SEO plugins and lots more…