Core SEO

The core practices of good SEO are fairly simple:

Avoid certain over aggressive SEO practices, which can get your sites blacklisted by the search engines
Understand how your pages are viewed by search engine
Take some steps to make sure your pages are optimized from the viewpoint of these search engines
From a broader viewpoint, good SEO involves creating an effective business campaign:

understanding your sales benefits and proposition,
being better at what you do than your competitor,
and creating a strategy for drawing and converting prospects,