According to the Wikipedia the SEO can be defined as:

Search engine optimization (SEO) is the process of improving the volume and quality of traffic to a web site from search engines via “natural” (”organic” or “algorithmic”) search results. Typically, the earlier a site appears in the search results list, the more visitors it will receive from the search engine. SEO may target different kinds of search, including image search, local search, and industry-specific vertical search engines.

Here are some good tips to increase the SEO of your site, so that you get the maximum number of visitors on your site.

• Keyword research is the first step in SEO. Take the time to figure out what words are used by the people you want to visit your site, and then use these words on the relevant page. In particular, make sure you use these keywords in the first few words of your page title because this is the most important bit of the page from a search engine’s perspective.
• Get trustworthy advice from SEO sources on the web. Unfortunately, not everyone knows as much as they say they do online and far too often SEO forums are full of bad advice; choose your sources well. A few we recommend: Google engineer Matt Cutts’ blog, Search Engine Journal, SEOmoz and of course, Search Engine Land.
• Look after your code. This means building a website that is easy for the search engines to understand. Your website should make use of up-to-date technologies like Cascading Style Sheets (CSS) to minimize the amount of formatting in the HTML page code.
• Make navigation easy. You can do this by building clear text links to all parts of your site. Search engines can’t follow image links or clever animated links like Flash; they like their navigation plain and simple—and so do many users.
• Get links from trusted, relevant sources. Links are like a vote for your site and you can’t rank well without them. Unfortunately, buying links or being indiscriminate in the places you link to and places you request links from, is no longer a good way to raise the importance of your site; think quality not quantity. Links must be relevant to the content of your site and they must be from reputable websites.