This is a very good guide for basic SEO for every website. SiteProNews usually has all the answers.
7 Questions to Evaluate the SEO Health of Your Website - SiteProNews: Let me start by saying that there is no perfect website. Not from an SEO point of view and not from any other point of view. I’m willing to bet that even the “big” ones have a few skeletons in their HTML code, a typo in their content or a few 404s. After all, if the likes of Facebook and Google get buggy sometimes,