I would say the first thing is to make sure that you have proper ventilation since you are over a garage (carbon monoxide, fumes from stuff stored in garage, etc) . That can be a very dangerous situation of not built correctly. I second the energy star rec. If you can afford argon-filled windows they are a huge help. We didn't splurge on them, but my brother did & it is amazing how they are warm to the touch when it is 30 degrees outside. Use materials that don't off-gas, low VOC paints (Sherwin williams has a good line). Wood floors are a better choice than carpet. As prev mentioend, bamboo is easily renewable. But even using cabin grade oak is better. That is irregular & slightly damaged wood that would be discarded if not used. If you have gas, a tankless water heater is great (they heat on-demand). But if you are all electric like us they are actually very inefficient. They take three breakers to operate! You can also use 6 inch exterior walls instead of 4 inch. You'd be surprized how much this saves on heating & cooling. It is a little added expense for framing, but well worth it.