Being Yahoo! Directory Listed

Importance: Low

Type: Trust

The Yahoo! Directory has been cataloging sites for a long period of time, and many believe that because of that, being listed can rank you higher.

Schema.org

Importance: High

Type: User Experience

Schema are used by major search engines like Bing, Google, Yahoo! and Yandex to improve the display of search results, so that their user has an easier time finding the right Web pages.

Schemas are classified as types and under each type there are properties. A full listof schemas can be found at http://schema.org/

If you are a WordPress user, you might be interested in the Gensis Framework by StudioPress, which comes with schema and is SEO optimized.

http://my.studiopress.com/themes/genesis/

User Generated Content Links

Importance: High

Type: Relevancy and Quality

Search engines are able to recognize links that have been generated through software.

An example of this is the hosted version of WordPress, wordpress.com, where they list the latest updated blogs on their network, through software, compared to links manually inserted in those blogs.

Nofollow Links

Importance: Medium

Type: Relevancy and Quality

Search engines, in general, don’t follow links with a nofollow relationship.

Having a large amount of nofollow links may be seen as unnatural and decreases the amount of outbound links, which has a negative impact of rankings.

Guest Posts

Importance: Low

Type: Quality

Using guest posts can be a good thing if they are done right. Guest posts need to be relevant and of quality. Having links in the author/ bio section or author page can decrease your rankings if those links are not relevant, have a low pagerank or are not seen as useful or valuable.

How about getting your customers to write content for you? User-generated content is a great for  SEO and all you have to do is ask for it.