Avoid 50-100 year mistakes.
Ensure that long-term infrastructure, especially buildings, are sustainable from the very start.
Ongoing green building programs address sustainability.
There are a number of items that can be done that require a little extra expenditure up front but will reduce fossil fuel use for the life of the building -- solar thermal on multi-unit residential buildings is one such approach (My company installs commercial scale solar thermal so I am biased). It does not fit into the standard 5yr simple payback required of most investors.