Overview of the main steps to good Search Engine Optimization

Content is King, write good, unique, and valuable content that will generate reputable back-links, spur forum discussions linking back to you, and return visitors as opposed to writing or doign SEO just for SEO (narrow focussed and for the wrong ends)
Think about the focus of each document before hand and consider keywords, related documents, and a call to actions.
Make sure that all the META elements focus and are relevant to the subject fo the content and the keywords (reinforce the subject) i.e keyword focus should be consistent in the title, description, H tags/subtitles, links, controlled back-links, Meta keywords

Markup your content in a way that spiders and minimal browsers can identify the hierarchy, and important (H-headers, P, Acronyms, Strong, EM etc)
Use accessibility attributes to provide pertinent information such as anchor titles, ALT, label values for form field labels. more importantly, do not stuff these attributes with senseless keywords compromising accessibility for SEO - SE intelligence will catch up with these in the near future
Create clean frontend markup code and maintain accessibility for objects that spiders cannot read

Along with each document, list relevant internal documents documents for further reading, and for intra-site cross-linking
Use a tag-cloud to point to related subjects and keyword focused document taxonomies to create a strong link within related documents
Proper management of 404 and 403 errors to point to relevant information
Natural keyword search within the site MUST be available
Friendly URLS are a must and should be customizable and contain keywords and easy to remember when used on print
URLs must nevr change, When they happen to, 301 and 302 redirects should be used to redirect traffic and properly update search engines
XML sitemap is an easy way to get Google and Yahoo to find all your site-pages

Measure and understand where the highest conversion rates come from and focus on enhancing traffic from those areas
Recognise the low conversion traffic sources and see if they can be improved upon, or if the traffic is just not suited for the targets (Promos, feedback, etc)
Periodically employ live tracking of traffic (click heatmaps) to see how random shoppers behave and click around - do this within each traffic source and audience segment to better understand how to position and write content-pieces (can also help decide link colour accessibility)

Have an effective CRM strategy in place that has virtually no leakages or neglected traffic/prospects
Evaluate which, and why some traffic may convert slowly (some industries are not quick), and device cultivation techniques to keep prospects interested and feeling valued through the cultivation and post-purchase process with overwhelming them with messaging
For lost prospects find ouwhy you lost them, if you can cross-sell better or listed to their feedback

Use SEM only as a short-term and supplement to organic SEO. It is expensive, and the more popular and lucrative the keywords/terms, the more expensive the practice will get and even eat into any profits you make