Search Engine Optimization

SEO consists in promoting a site, in particular by making it indexed
by search engines. Optimizing is the art to improve the position of a
site among others in the list of results of search engines, which
answer a query.
Indexing

SEO is preceded by a phase of preparation of the site. The creation of
a sitemap of the site, the generation of meta-tags, which describe the
page for search engines, can be automated thanks to specialized and
free tools.
Then it consists in promoting the site and making it visible on the
Web, by registering it on search engines and directories, announcing
it on forums and magazines, and by obtaining backlinks from other
sites.

See the complete SEO manual for more infos.

The indexing of a page by an engine is accompanied by further
information on this one, such PageRanks, which is updated regularly,
and that webmasters try to improve by techniques of optimizing.
Optimizing

Optimizing for search engines, is the technique of webmasters to
obtain a better position in results of queries on Google and other
search engines. Only first pages of results make really traffic and
somtime, only the three first line bring visitors. This optimization
depends on some factors:
The domain name
It is a factor of selection of the site for the list of results, if it
contains keywords in connection with the query.
Titles
The keywords contained in the titles and subtitles have a bigger
importance than those which appear in the simple text.
Keywords
Certain words are more often requested to earch engines. It should be
made sure that the text contains all the words, with synonyms, which
belong about the article. To repeat many times a word does not have an
effect, on modern engines at least, but two or three occurrences can
be useful because the context where appears a word is taken into
account.
Filenames and anchors
They must also contain the keywords specific to the article (words
separated by a dash).
Links
The backlinks, links towards a page, if they are numerous and of value
(if they are linked themselves), improve the position in results of
engines, with equal contents.
Broken links are obviously to avoid and that requires a monthly
control at least.
PageRank.
Take part in position of a page in results of the search engines.
Duration of visits
Search engines can easily identify on the choice of a site in the list
of the result of a request. And the deadline between two clicks (for
the same Net surfer), and thus the duration of visit on a site. From
that they can evaluate the interest of a webpage. It is thus essential
that the contents are sufficiently interesting to retain the visitor.
The hosting
The fact that a domain name is associated to an IP address in a given
country could improve the position according to the language employed
for the request, or the regionality of the subject. Some hosts propose
the geolocalisation of the domain name, for professional hostings.