As promised, I'd explain what needs to be done while doing SEO.
Firstly, it depends on what Search Engine we optimize website for. Every Search Engine has its own ranking algorithm, so optimizing website for each of them is different.
Also, ranking algorithm of each SE is big secret and never revealed and is changing. So webmasters only guess what is important and try to do every thing what they think that important.
Anyway, we can expect that there are two big separated optimization steps: on-site and off-site optimizations that important for all Search Engines (Of course in different ratio for different search Engine).
On-site SEO means we optimize every thing on our website.
Of-site SEO means we create connection our website with another websites on the WWW, (we call link building process).
That's all for this leason :) , I'm a little tired and can't give out of my head the winning sound of cuocthiseo contest :D .