Search engines classify your site depending on its content, they realize if you offer something new, good and unique or not.
Give the rest of the world a reason to link to you. The more incoming links you get,
the more your pagerank and traffic are increased.
Use B tags around some of your keywords on each page, but don't use them everywhere a keyword appears,
remember you are writing for humans, not for search engines.
You can use header tags (H1, H2...) to include some of them too.
If you have several topics that could be sepparated without any problem, it might be worth having multiple domains
since most search engines will only list one page per domain for a given user search.
Whenever you send descriptions of your site, i.e. submitting to a directory,
don't give always the same link text, try to use different words each time.
If search engines see the same links or descriptions of your site continually,
they might think you are using automated programs to promote it.
Use titles for links. This will help people know where you are sending them, and some search engines
use this to calculate the relevancy of a page for a given search.
If you own a big site, with lots of pages, it would be nice to include a site map.
Site map should be linked from every page of your site. This will help the search engine robots find all pages easily.
Do not hide links with the intention of promoting (i.e. using the same background color as the link text color).
Search engines will notice and they won't like it.
Do not duplicate pages. Even if there are only little changes between them.
Be careful with dynamic pages, if the same page can be generated with different URLs and they get indexed,
there will be duplicated pages of your site on the search engine index.
Images, Flash or JavaScript are not understood by search engines.
If your site depends a lot on them, add some text too.
Exchange links with sites that have similar content than yours.
Not only this will help your visitors, but you will get additional traffic from other sites and your pagerank will grow up too.
Your domain name is very important, remember it will be one of the first things
surfers will see about your website, so it has to describe some of the content you are going to offer them.
Choose page names relevant to their content. If a certain page provides cake recipes for children
then it should be named something like "children-cake-recipes.html", not "45_1.html" or "recipes25.html".
Text navigation is better than image navigation. Text navigation will help search engines
understand the content better, thus increasing your position for a particular keyword search.
Meta keywords are important. You may need to use
Google's AdWords Keyword Tool
or another keyword related software if you are not able to discover enough keywords for your site.
Use a relevant title and meta description on every page.
The page title is one of the most important SEO factors.
The meta description tag will appear as the descriptive text below your listing,
so it should include the relevant keywords and be written so as to make searchers to click on your listing.