Just came across an interesting article that provides some good tips for people looking a simple checklist of the key areas to review with regards to SEO. The main parts are:
1. URL canonicalization and 301 re-directions.
2. Unique Title Tags and Meta Data.
3. Search Engine Friendly.
4. Has the site been submitted to Google Webmaster Central?
5. Check for Duplicate Content.
There are also details for each section that are in this article called "5 Minute SEO Site Audit".
Also there is a tendancy to see SEO as the "be all and end all" solution when behavioural targeting versus SEO is a subject I would recommend you look into