When you go grocery shopping use a canvas bag that can be used over and over again instead of using the free plastic/paper bags on offer at the counter.

Reuse plastic bags, and store them in an old plastic bottle - chop both ends off the bottle and pull them out of the spout end when you need them! 
 
Ensure you inspect the energy requirements of any new appliance you buy - efficient, modern fridges, freezers and dishwashers etc are much better than old ones! 
 
Wash your clothes on the lowest setting you can get away with, and try it with less detergent - you'll be amazed how little is actually needed!