Useful Tips for SEO by Maile Ohye, a developer advocate on Google's Webmaster Central Team

1. 301 redirect to preferred domain (www version or not)
2. Verify ownership of site in Webmaster Tools (set up e-mail forwarding for any issue reports)
3. Background check domain name (site:domain.com)
4. Fetch as Googlebot
5. Include analytics code
6. Strategic site design
   1. Appeal to target audience
   2. Focused content
   3. User Experience
7. Define conversions:
   1. Newsletter Signup
   2. Contact sales lead
   3. Buy product
   4. Share product
8. Keyword based copy
   1. Unique Topic
   2. Unique Title
   3. Unique meta description
   4. Non-dynamic sites; keywords in url, hyphen separated
   5. Descriptive anchor text (avoid "click here")
9. Use social media to drive interest

If you haven't tried it - you should! Google page speed takes a quick run through your site and checks on the performance.
It returns some great data and suggestions for optimizing your code, especially useful for optimizing mobile web pages.