About the basics
Do you need an SEO ? Useful tips from Google.
Going pro
When searching information about SEO and SEM, I came across with WPO. Web Performance Optimization.Almost every WPO tool out there provides a Timeline or Waterfall Chart. It is great to learn how your page actually gets loaded by the browser. Which resources are depending on each other, how does JavaScript impact page load and how much rendering is going on.
So SEO and SEM are making sure, that your page is out there to be found and WPO makes sure your site actually works (fast). Because what's the point, that people find your sites and want to buy, but can't access?
Worst case scenario a.k.a Hullut Päivät
more about WPO here