SEO Tutorial
Inbound and Outbound Links
Many sites linking to your site helps legitimize it, unless you link back to all the same sites. Then search engines assume that your reciprocal links are a contrivance. Sites which exist only to prop up other sites by creating artificial inbound links are known as links farm. This definitely comes under the category of black hat SEO. My Kierkegaard site has a couple dozen links to other sites, but there are hundreds of sites that link to it. While it is good to have many sites link to your home page, it is good to have links pointing to important parts of your site. Internal links are helpful, especially in natural language, as well as links in navigation and in a general site map.
Not all inbound links are equal. If they come from a site with an edu or gov extention they possess greater SEO weight, in that these sources have greater trustworthiness.
Spaces should never be in a filename because they will be turned into the characters "20%". Hyphens are better than underscores because underscores are used in programming and are words so conjoined are considered to be one word.
Longevity
It is often assumed that the longevity of a site helps its ranking. I too assume that this is true. At the very least there seems to be a waiting period. I suppose that search engines want to ensure that a fly-by-night site does not get ranked prematurely. This might also be due to the fact that some black hat developers will take an article, re-word it slightly, and then post it with the intention of giving the inherent keywords more weight, which is known as article spinning. Again, search engines possess complex algorithms that can detect this sort of practice.
Similar to longevity the length of time that your domain is registered for. Search engines can assume that if you purchase only a year at a time that your site might be a fly-by-night affair.
Fresh versus Stale Content
This topic certainly qualifies as an SEO myth. It is often said that content needs to be refreshed often, else a page's rankings will drop. I have found from my experience that there is no truth to this. I cited the Kierkegaard site above with stale content. That site has broken images, and has not been updated in years, so far as I know.
File Size
It is generally agreed that the more content a page has the less important that content is further down the page. Content closer to the top of the page is ranked higher. It might be best to break up long pages into smaller files. Smaller pages also have the added benefit of being more accessible for someone tabbing through the page with a keyboard. Also, smaller pages decrease page load time. Factors that increase page size include hidden input tags in forms that contain hundreds of characters, excessive HTML comments, and heavy-handed HTML structure. A balance must be struck.
rel="nofollow"
In 2005 Google started encouraging webmasters to use the rel attribute with the value "nofollow" for links that they wanted Google not to index. This is seen as a useful precaution against spammers who come to blogs and post URLs. It is also intended to hide parts of the site that are not important to indexing, such as a signin page or a purchase sequence. The rel attribute is acceptable HTML, but some have argued that the "nofollow" attribute is counterintuitive. The rel attribute describes the relationship between the link and the document. The value is saying in essence that there is no relationship. Johan Petersson has written a helpful short article on this.