Tom is arguing that energy is a good place to start, purely because it's easy to measure...
If you cannot measure it, you cannot improve it. - Lord Kelvin
Interestingly it turns out that improving the efficiency of out devices actually increases our use of energy on the macro scale, so we need not only energy efficiency, but energy literacy.
But we also need other forms of literacy. Material literacy, what materials are you using? What are they composed of, and how toxic are they? But you need to think about not only what's in your product, but what it takes to produce it.
Production literacy, where is your product produced, how is it produced, who makes it and how far does it get transported? We need to think about whether we need to make a product before we make it.
Beyond that we get into resource literacy. Geeks love systems, and this is a system that's yet to be explored. The USGS has estimated that e-waste with have between 40 and 100 times the amount of gold in it than ore dug out of a gold mine. People are starting to get interested in this...
In order to close the loop with recycling, the people that un-make things need to know how we made them in the first place.
Finally there is 'legacy literacy'. We inherit a lot from industrial design, and its a profession that developed partially in response to American overproduction in the early 20th century. Gillette selling razors at a loss, and selling you a life time supply of razor blades for a healthy profit, is the obvious example.
Reduce, reuse and research. The idea of reusing tools, before building your own. Don't build a distributed sensor network, use cell phones, the network already exists. Just hook your sensors up to the cell network.