Search engines determine the importance of your site by finding out who is linking to you. If a trusted library, college, municipality, government, high ranking business or organization links to your site, you are going to have an easier time finding your desired rankings. The alternative is to get several personal websites, blogs and forums to link to your website you to get the attention of the search engine that other people (or sites) find your site important.
There are several directories that you can include your site in that can be helpful but they should only play a part in your linking strategy. Human edited directories are the most desired like Yahoo Directory and DMOZ as they have the size and scope that search engines trust. Logic being, if they trust your site, then I do to. There are many directories that allow you to input your site information automatically which can be helpful.
If you can post and keep a link on Wikipedia it can be helpful to capture traffic but the weight of page rank will not follow because Wikipedia blocks that aspect of it with No Follow tags on their links. Requesting links from private and public website can be a good strategy as many webmasters like to have the most complete listing of a certain topic.
Getting natural links from a wide variety of pages is extremely important and failure to do so will impede you in your goals. Search engines can store the date that new links are discovered. From that they can determine when an artificial link campaign has occurred. People the buy links for their domain are sure to be discovered and penalized by the search engines. The only way to benefit from incoming links is to have people want to naturally link to your site. Of course you can send people emails making them aware of your site, but do it steadily and over a long period of time.
Blue Backlinks: http://www.bluebacklinks.com - A great website for checking what websites are linking to your website. You can also use it to see who is linking to your competitors, websites you might want to create a relationship with, or websites targeting the customers you want to reach. Websites that link to your competitors are great places to start creating relationships for your website, books, or authors.