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 for targeted keywords. Usually, the earlier a site is presented in the search results or the higher it "ranks", the more searchers will visit that site. SEO can also target different kinds of search, including image search, local search, and industry-specific vertical search engines ( taken from: http://en.wikipedia.org/wiki/Search_engine_optimization).

Techniques:

there are 2 commons techniques that are used on SEO, white and black hat. the technique name said it all, white is the "good" way doing SEO, but it may need more time ..:). Black hat is "bad" way but FAST to get your web/blog indexed in search engine.

white hat

Research A Profitable Niche Market
Do some research first before you build your website, including the market and the most important is your KEYWORD

Creating & Tuning Your Blogs/ website
ofcourse you must create your blog or website. including:

• w3c standard
• put h1,h2,h3
• title as the keyword
• and so on

Posting Free Valuable Content Your Readers Will Love
Title said all.. 

Interlinking Your Blogs / websites
make your individual blogs/ website them into a network.

Monetizing Your Blogs / website 
by placing ads on your blogs or websites. 

black hat

Mass Blog Networks
Creating huge networks blogs, the HUGE is 100+ blogs. all blog will link to 1 main blog and have the same keyword.

Stealing High Ranking Blogs
Steal the word or keyword from high rank blogs that has been deleted.

Redirecting Blogs
Create the blog only for redirect… maybe to your blog or even to your affiliate page

Blog Comment Links
Post comments on high rank blog and link it to you page.