I read books and tutorials. Then it's practice, practice, practice.... I had a lot of time to practice on my own while in school. :D This might help as well http://lounge.ego-farms.com/
I went to a school, and was taught a couple of classes on the basics. Then I practiced, and I learned everything else that got me to my current level. Practice Practice Practice. It's the best way to learn.
It's good practice to triangulate. However, your low poly wireframe shows some polys triangulated and others not. Are you sure you're triangulating the entire mesh?