What is your suggestion to learn these techniques? Just through experience or should I pick up books on it?
In order to learn from experience, you have to have someone teaching you. If you want to really improve your skill, learning by your self isn't enough.
Ideally it's nice to have a mentor and/or buddy you can bounce ideas off and experiment with.
Based on your samples, you have a good eye now its time to put it to use with the camera. D40 is a decent enough body to start and get you going plus 18-200 is another great toy. Boost the sharpness in-camera and that lens (soft by default) will be your best friend for very long time.
For books:
There are THOUSANDS of books out there and yes I do recommend you get one and/or get many.
Few popular books are understand the exposure by brian p-something, another one is by Steve Sint - don't remember the name of his latest book but i love his explanation (you can find him on amazon). For online stuff, I like David Ziser's blog as well as the whole kelby training lessons. Lynda.com also provides really good tutorials.
Iif you want, PM me, we'll talk more. I also have bunch of reading material that you might like. Good Luck