SEO Basics (search engine optimization)

This article will cover the why, what and how of SEO (Search Engine Optimization). 

What exactly is SEO?
Each search engine (e.g. Google, Yahoo!, Bing, etc) ranks web sites and lists them in their engines according to that ranking. The engines decide which criteria to use when ranking sites.  Some factors are well known.  Others are more obscure and mysterious. The SEO Expert’s job is to reverse engineer each engine’s process, then apply whatever knowledge they glean to your site so that it is more palatable to that particular engine.  When properly optimized, a site has a greater chance of a higher ranking.

Why is SEO important?
A site that is well optimized for search engines will receive more ‘organic’ traffic.  ‘Organic’ means your site will come up naturally when somebody types your keywords in an engine, as opposed (or in addition) to it coming up as the result of a paid ad in the engine’s sidebar.  In addition, following a search engine’s standards often results in a better looking web site, which translates to a better web experience for your site visitors.

How is SEO done?
There are two facets to how SEO is performed; common sense tasks, and technical tasks. 
Tasks under ‘common sense’ include making the site look better, ensuring it appears legitimate and offers a pleasant surfing experience for the user.  For instance, the site should have an About Us page, a Privacy Policy, a Contact Form, etc.  Make sure the navigational structure is functional and easy to use.  Also, spend time seriously considering which keywords you wish to promote, and choose them wisely.  Study your competition and take notes.  Studying your competition and trying to understand how they achieved their high ranking is one of the best things you can do.
The technical side includes the following key elements:

• Choose your article’s URL wisely. Place keywords within the URL, of your articles, when possible.
• Encourage as many back links as you can.  A back link is a link on someone else’s site pointing back to yours.  Google sees back links as a vote of confidence for your site.  The more you have, the more relevant you become. Not all back links are equal.  Try to get back links from larger, more reputable sites when possible.
• Ensure the HTML in your site is as search engine friendly as possible.  For instance, make certain every page uses title tags with keywords in those tags.  Use META tags (description and keywords) on every page, and take advantage of image tags, inserting keywords where appropriate.  The page content should also include your keywords several times, but without overwhelming the text.  Density is important.  The keywords should be heavily present, but not obviously overdone.
• Finally, carefully choose a relevant domain name that reflects your brand or products and is easy for people to remember.

Always keep SEO in mind as you build your site.  A well optimized web site which looks natural and unforced is well worth the effort.  The search engines will reward you in time!

References:
My constantly updated SEO Tips page

Matt Cutts (Google) How important is it to have keywords in a domain name (video)?